Here’s a startling fact: For every one human cell we have, there are ten bacteria cells in our body to match it. That means that the majority of DNA in our body isn’t even human; it’s from the 500 bacteria species that call us home.1 Thinking about that much bacteria might have your skin crawling, but the relationship between human and bacteria is really a perfect synergy: we give bacteria room and board, and in return, they work hard to protect our intestinal health, which ultimately protects the health of our immune system and overall well-being. But if we have that much bacteria already living in our gut, you might be thinking to yourself, what are probiotics’ benefits?

That said, supplements with higher numbers of CFUs are sometimes used to treat conditions such as irritable bowel syndrome (IBS), allergies, and respiratory illness. While probiotics have generally been found to be safe for most people with normal immune systems, too much can cause gas and upset stomach. We narrowed our search to supplements with dosages between 1 billion and 100 billion CFUs. 

Though most probiotics are formulated for both men and women, Garden of Life’s Raw Probiotics for Women is manufactured with women in mind. This probiotic has a whopping 85 billion live cultures and 32 different probiotic strains to target everything from gut and vaginal health to thyroid and nutrient absorption. It contains two popular probiotics, Lactobacillus acidophilus and Bifidobacterium, and is gluten-free, soy-free, and made without fillers or binder—which is great for anyone with dietary restrictions or allergies. Each container comes with 90 capsules; the recommended dose is three capsules per day.
Like some of the other probiotics we’ve reviewed, the HyperBiotics PRO-Women Probiotics with Cranberry Extract and D-Mannose do not need to be refrigerated in between uses. What sets this particular formula apart though is its longer shelf life made possible by the patented HyperBiotics ‘LiveBac’ manufacturing process. In fact, the HyperBiotics PRO-Women Probiotics formula can usually last for more than a year when stored in normal indoor conditions!
When it comes to feminine health, the focus is all about balance. Whether you are trying to starve off annoying yeast infections and BV or recurrent urinary tract infections, the secret to optimal health lies in balancing out the bacteria that are already in your system. That’s why these vH Probiotics with Prebiotics and Cranberry contain prebiotic compounds to promote the growth of good bacteria in the digestive and reproductive systems.

Eating more foods that are naturally rich in probiotics, like yogurt, kimchi and kefir, can help restore balance in your gut and create more “good” bacteria to fight off inflammation from “bad” bacteria. But what about food products that have probiotics infused into them? Indeed, manufacturers are banking on a new crop of gut-friendly products. From chocolates and granola bars to juices and tonics, nut butters, bottled water and even air sprays, you can’t escape the probiotic movement.
Other uses. Many other claims are made for probiotics—that they lower cholesterol, alleviate allergic skin conditions (like eczema), treat ulcers and urinary tract infections, improve vaginal health, reduce the risk of colon cancer, ease anxiety and depression, and ward off traveler’s diarrhea. Good evidence to support these claims is lacking. Research on probiotics for weight loss has yielded inconsistent results, and even studies with positive results have mostly found very small benefits, as was seen in an analysis of 15 clinical trials in Obesity Reviews in 2018.
Niv Zmora, Gili Zilberman-Schapira, Jotham Suez, Uria Mor, Mally Dori-Bachash, Stavros Bashiardes, Eran Kotler, Maya Zur, Dana Regev-Lehavi, Rotem Ben-Zeev Brik, Sara Federici, Yotam Cohen, Raquel Linevsky, Daphna Rothschild, Andreas E. Moor, Shani Ben-Moshe, Alon Harmelin, Shalev Itzkovitz, Nitsan Maharshak, Oren Shibolet, Hagit Shapiro, Meirav Pevsner-Fischer, Itai Sharon, Zamir Halpern, Eran Segal, Eran Elinav. Personalized Gut Mucosal Colonization Resistance to Empiric Probiotics Is Associated with Unique Host and Microbiome Features. Cell, 2018; 174 (6): 1388 DOI: 10.1016/j.cell.2018.08.041

When seeking out the best probiotic for you, consider your overall health, dietary needs, antibiotic use, GI challenges, and similar concerns. Then, review our list of the ten best probiotic supplements, which offer everything from raw probiotics, which must be refrigerated, to shelf-stable, slow-release probiotics that concentrate fewer CFUs in tiny, once-daily capsules.


This story has played out before, most notably with vitamin supplements, which decades of research have revealed to be completely unnecessary for most adults and, in some cases, dangerous, correlating with higher rates of lung, breast and prostate cancers. But that has not stopped marketers from pushing another nutritional craze. According to a National Institutes of Health survey, the number of adults in the U.S. taking probiotics or their cousins, prebiotics (typically nondigestible fibers that favor the development of gut bacteria), more than quadrupled between 2007 and 2012, from 865,000 people to nearly four million. San Francisco–based business consulting firm Grand View Research estimates that the global probiotics market exceeded $35 billion in 2015 and predicts that it will reach $66 billion by 2024.
What about prebiotics vs probiotics? Prebiotics are the food fibers that go through the gut unchanged and are then used by good colon bacteria as a food source for their own growth. Everyone already has most of these good bacteria present, but often in small quantities. Prebiotics are used to stimulate their growth. Simply stated, you already grow your own probiotics within your colon. You do not rely on them to make the passage through the stomach acid — acid that can destroy many probiotic bacteria. That’s why taking a probiotic supplement or adding probiotic foods to your diet does not always help your digestive system. You can eat as many probiotic bacteria as you want, but if they don’t survive the trip to the colon, your effort will be fruitless.
Large bodies of evidence suggest that probiotics are effective against several forms of diarrhea, including antibiotic-associated diarrhea, acute diarrhea, traveler’s diarrhea, infectious diarrhea and other associated diarrhea symptoms. They also help with constipation relief. Probiotics have also been found in meta-analyses to reduce the pain and severity of irritable bowel syndrome (IBS) symptoms, aid in the eradication of H. pylori and treat pouchitis, a condition that occurs after the surgical removal of the large intestine and rectum.
If you get sick often, probiotics might be the immune booster you've been looking for. The Cleveland Clinic says they've been shown to strengthen immunity by enriching and replenishing the good bacteria in the body. And when you eat foods with probiotics regularly, it's easier for your body to produce vitamins and enzymes that help keep your intestines happy.
Most of the prebiotics identified are oligosaccharides. They are resistant to the human digestive enzymes that work on all other carbohydrates. This means that they pass through the upper GI system without being digested. They then get fermented in the lower colon and produce short-chain fatty acids that will then nourish the beneficial microbiota that live there. Oligosaccharides can be synthesized or obtained from natural sources. These sources include asparagus, artichoke, bamboo shoots, banana, barley, chicory, leeks, garlic, honey, lentils, milk, mustards, onion, rye, soybean, sugar beet, sugarcane juice, tomato, wheat, and yacón. The health benefits from these oligosaccharides is a topic of ongoing research.

Probiotic supplements are not drugs (in the United States), although super potent forms may be obtained through prescription. As such, they are not intended to treat or cure any diseases, mental or physical. Probiotics benefit and complement a healthy way of life filled with nutritious food, adequate exercise, restorative sleep, beneficial social engagements, reduced exposure to toxins, and hydration with clean water.
To factor strain-specific benefits into our efficacy score, we referenced the information in these guides. Products were rewarded for containing strains on these lists. Additionally, measured levels of each strain were compared to what is thought to be effective based on these guides, and scores were scaled accordingly. In cases where products did not list strain-specific amounts, or their listed strains were not included in these guides, total measured CFUs were compared to a general effectiveness threshold of 1 billion CFUs cited by research published in the American Journal of Clinical Nutrition11.

Studies have shown some benefits linked to Lactobacillus and treating and/or preventing yeast infections, bacterial vaginosis, urinary tract infection, irritable bowel syndrome, antibiotic-related diarrhea, traveler's diarrhea, diarrhea resulting from Clostridium difficile, treating lactose intolerance, skin disorders (fever blisters, eczema, acne, and canker sores), and prevention of respiratory infections.
They can break down substances in foods that keep you from absorbing the micronutrients inside. They not only protect against the consequences of rogue molecules passing through a leaky gut, but they assist your intestinal cells in staying healthy to optimize nutrient absorption. In addition, some of the metabolic by-products of probiotics, such as short-chain fatty acids and vitamin production, are very nourishing to your GI tract.
Quick note about some formulations with multiple strains (including this one): Take a look at the label below and you’ll see that the supplement contains a mix of strains, but the label just says there is a total of 20 billion CFUs (how they measure the amount of bacteria). This does not tell us how much of each particular strain there is, and we want to know that there are at least 1 billion CFUs per strain to get a beneficial effect.
Back to the question of what are probiotics: There are five main types, each in its own classification called a genus. Within each genus there are multiple species, and within those species there are multiple strains. For example, Lactobacillus is a very common genus of probiotics. Within that genus are numerous species, such as rhamnosus. The genus and species of a microbe are always italicized, making it easy to know that a microbe is involved. In a species such as Lactobacillus rhamnosus (often abbreviated L. rhamnosus), there are many strains. An example of the name of a strain is L. rhamnosus GR-1.

However, a 2003 pilot study and 2011 randomized, controlled trial both reported that RA activities remained unchanged, but the subjects treated with probiotics reported statistically significantly higher levels of “subjective well-being.” One suggested reason for this was that the trials were too short to establish changes in the observable changes in the internal earmarks of RA.
Align uses the patented probiotic strain Bifidobacterium, which helps to maintain a healthy digestive system and digestive balance. It contains 1 billion CFUs when manufactured, and 10 million CFUs when used by the best by date. (Very often, the number of CFUs in a product decreases over time.) If you have trouble digesting certain foods such as caffeine or dairy, this will be a good option for you.
The second type of probiotics are soil-based organisms (SBO), which tend to be more resistant to acid in the gut. Here’s the thinking behind soil-based probiotics: Many people (particularly in the paleo community) believe that widespread gut and health issues today are the result of life in a too-clean society. In the past, when more people worked in the dirt, played in the dirt, there was less obsessing over cleanliness and antibacterial products, we got more natural exposure to probiotics. The benefit of soil-based probiotics is that they come from the earth, and the bacteria (which are still living) have their own natural, protective capsule surrounding them. I recommend soil-based probiotics to patients with autoimmunity, in addition to the classic form. They are particularly helpful for people with SIBO (small intestinal bacterial overgrowth)—with SIBO, you also have an overgrowth of good bacteria; and in this case, the classic form of probiotic is not what you need to fight the infection.

MegaFood is our only top pick that’s certified vegan, as well as being gluten free and dairy free, making it a good choice for any food-sensitive or vegan probiotic seeker. It has fewer of our wishlist “general health” strains than Vita Miracle, but it still contains five. This could be a go-to if you eat vegan, even if you’re not recovering post-antibiotic.


Probiotics are clearly incredibly supportive, but they can't do their work alone. To make sure that you're getting the most out of your microbes, it's important that you give them the support they need to work. You've got lots of options for supporting your gut health, from dietary changes to probiotic supplementation, but make sure you're at least covering the following bases.

There are both probiotics and prebiotics in fermented foods. I differ from a lot of doctors in that I recommend that patients with infections like Candida and SIBO don’t eat prebiotics until they’ve cleared up the infection—because the prebiotics can feed those infections, too. I find that it’s better to get rid of those infections first, and then add in prebiotics to your diet after. [See here for more from Dr. Myers on treating yeast infections.]

The second Elinav study, “Post-Antibiotic Gut Mucosal Microbiome Reconstitution Is Impaired by Probiotics and Improved by Autologous FMT” involved a mouse model and human patients. One cohort of mice and a parallel human group was given the same probiotic strain used in the first study to see if they had more success repopulating their gut microbiota after a round of antibiotics. Another “watch-and-wait” cohort didn’t take probiotics to assist gut microbiome recovery after antibiotic-related depletion. A third cohort was given an “autologous fecal microbiome transplant” (aFMT) which consisted of a patient’s own gut microbiota that had been collected before he or she started a cycle of antibiotics.
Step No. 1 is consume more sour foods — it’s the top way probiotics benefits can be accessed. Embrace what I call “the power of sour” with sour foods like apple cider vinegar and fermented vegetables. They contain some probiotics, but also they contain certain types of acids like gluconic acid and acetic acid, healthy acids that support the function of probiotics (even functioning like prebiotics in some cases).

But before you start reaching for the calcium supplements, there may be a more effective way to support your bone health. Like many other parts of the body, the health of your bones is closely tied to the health of your gut, especially your intestines. Temporary intestinal inflammation can trigger an immune response in which your body releases interleukins, proteins that have an immune function but also absorb bone tissue. If the temporary inflammation remains unaddressed, these molecules can take a toll on your bones, eventually weakening them.14


Probiotics help tip the balance back in favor of the good bacteria. In doing so, they may provide some relief if you have irritable bowel syndrome (IBS), ulcerative colitis, acute infectious diarrhea, and diarrhea associated with antibiotic use or Clostridium difficile (C.diff) infection. They also can boost your immunity, fight inflammation and potentially have beneficial effects on cholesterol.
Walk into any grocery store, and you will likely find more than a few “probiotic” products brimming with so-called beneficial bacteria that are supposed to treat everything from constipation to obesity to depression. In addition to foods traditionally prepared with live bacterial cultures (such as yogurt and other fermented dairy products), consumers can now purchase probiotic capsules and pills, fruit juices, cereals, sausages, cookies, candy, granola bars and pet food. Indeed, the popularity of probiotics has grown so much in recent years that manufacturers have even added the microorganisms to cosmetics and mattresses.
Probiotics may also be of use in maintaining urogenital health. Like the intestinal tract, the vagina is a finely balanced ecosystem. The dominant Lactobacilli strains normally make it too acidic for harmful microorganisms to survive. But the system can be thrown out of balance by a number of factors, including antibiotics, spermicides, and birth control pills. Probiotic treatment that restores the balance of microflora may be helpful for such common female urogenital problems as bacterial vaginosis, yeast infection, and urinary tract infection.
Renew Life Ultimate Flora offers 30 billion CFUs with 10 scientifically studied strains of Bifidobacterium and Lactobacillus, which according to current scientific research, are the two most prevalent good bacteria found in a healthy gut. In other words, you might choose these if you’re seeking a careful balance designed to re-establish proper immune health and digestive equilibrium.
Anal itching is the irritation of the skin at the exit of the rectum, known as the anus, accompanied by the desire to scratch. Causes include everything from irritating foods we eat, to certain diseases, and infections. Treatment options include medicine including, local anesthetics, for example, lidocaine (Xylocaine), pramoxine (Fleet Pain-Relief), and benzocaine (Lanacane Maximum Strength), vasoconstrictors, for example, phenylephrine 0.25% (Medicone Suppository, Preparation H, Rectocaine), protectants, for example, glycerin, kaolin, lanolin, mineral oil (Balneol), astringents, for example, witch hazel and calamine, antiseptics, for example, boric acid and phenol, aeratolytics, for example, resorcinol, analgesics, for example, camphor and juniper tar, and
We are clearly getting to the strain level by going beyond “Saccharomyces boulardii” and to “Saccharomyces boulardii CNCM I-745”. They did a great job by actually putting it on the label so you don’t even have to contact the company to see exactly what strain you’re getting. (P.S. this is a well-researched strain that I highly recommend, especially for preventing antibiotic-associated diarrhea.)
You dread stepping on the scale and avoid looking at your profile in the mirror because you know you gained weight and need to lose some. You tried every diet on the market to no avail. Your frustration level is high, but you do not need to give up hope. The first thing to do is to love yourself regardless of your weight so that your emotions and stress levels do not sabotage your efforts. You can love yourself while working toward self-improvement.
If that's not enough, your doctor may also suggest a probiotic supplement. But don't go and grab just anything off the pharmacy shelf. Probiotic supplements are not all the same, and they often contain different strains to serve different needs, says naturopathic physician Amy Fasig. Example: What one person gets to battle strep throat is different from what would be prescribed for someone suffering from Irritable Bowel Syndrome, she says.
Dr. Tobias responded with Deep Immune Support, a shelf-stable capsule that does not require refrigeration and employs four acid-resistant probiotic strains. One such strain: DE111, a highly effective spore-forming probiotic, which complements and balances the non-spore strains most commonly found today, and also supports the proliferation of beneficial bacteria. The patented, delayed-release capsules are made in the USA and are both kosher and vegetarian.
Best Probiotic says that Suprema Dophilus, manufactured and distributed by Vitabase, enjoys the highest customer rating in the market. Specially coated to help the bacteria spread through your entire digestive tract, its website claims over four billion viable cells per capsule, including five lactobacillus strains and three bifidobacteria cultures. Best Probiotic says that Suprema Dophilus also contains fructo-oligosaccarides to increase the life span of the bacteria.
"In fact," she continues, "80% of immune system cells are found in the gut. In addition to the well-known GI benefits of minimizing bloat, gas, constipation, and diarrhea, probiotics aid in digestion by extracting nutrients, helping your body absorb minerals, produce vitamins, and make brain chemicals, including over 30 neurotransmitters along with mood-enhancing serotonin. A healthy person has over 100 trillion microbes, generally a five to one ratio of helpful to harmful."
Probiotics stick around for a while, though for how long isn’t precisely clear. You have to keep taking them to continue to reap the benefits. Further, getting a wide variety of strains into your system is beneficial. “Periodically mixing up your probiotic supplement is also a good way to ensure that you get different health-building strains in your health regime,” says Dr. Cook.
Rachel Allen is a writer at Hyperbiotics who's absolutely obsessed with learning about how our bodies work. She's fascinated by the latest research on bacteria and the role they play in health, and loves to help others learn about how probiotics can help the body get back in balance. For more ideas on how you can benefit from the power of probiotics and live healthier days, be sure to subscribe to our newsletter. To learn more about how a healthy microbiome can enrich your life, subscribe to our newsletter.
Remember, while bacteria gets a bad rap, not all bacteria is bad: As New York City-based certified dietitian-nutritionist Gina Keatley tells Allure, plenty of microorganisms, including probiotics, actually help your body function. "Probiotics may help stabilize the protective barrier in our gut so bad microorganisms don't take root, stimulate the immune response, and aid in production of vitamins, such as vitamin K," she says. Sonya Angelone, a registered dietitian and Academy of Nutrition and Dietetics spokeswoman, adds that while we have more to learn about the role of probiotics, beneficial bacteria is understood to help crowd out harmful bacteria in our bodies. This good bacteria may also help lower cholesterol, aid in reducing colds and acute respiratory infections, and reduce the occurrence of vaginal yeast infections, she says.
The Bifidobacteria (Bifidus) predominantly live in your colon or large intestine. They produce the very important short-chain fatty acid butyrate, which supplies energy to your colon cells to keep them functioning optimally. But butyrate also gets absorbed by the body, regulating a variety of metabolic processes, including your sensitivity to the hormone insulin (which regulates blood sugar) and even memory formation in the brain. The most beneficial of these are B. lactis and B. longum. Research shows the benefits for Bifidobacteria include reducing inflammatory bowel disease and several cancers, especially colon cancer. Another study showed that a specific strain of Bifidobacterium lactis helped control body fat mass and reduced waist circumference and food intake.
​​​​​​Every woman’s microbiota is different and so results will vary. However clinical studies using the blend of probiotic strains in AZO Complete Feminine BalanceTM demonstrated benefits in as little as 7 days. We suggest continuing with use of the product for a minimum of 30 days. Also, keep in mind that for regular maintenance, you may not SEE results but the product is still helping to protect and maintain a healthy vaginal flora.*
Prebiotic fibers are the non-digestible parts of food that are typically found in fruits, vegetables, and legumes. These fibers act as food for the healthy bacteria in your gut, and are an essential part of the digestive process. That’s why the Vitamin Bounty Women’s Pro-Daily Probiotic contains prebiotics and probiotics for a truly complete formula that helps ease digestive issues while also maintaining proper feminine health.

Most recently, two back-to-back papers were published simultaneously on September 6 in the journal Cell showing that many people can’t successfully colonize standard probiotic microbiome in their gut. The scientists also found that consuming generic probiotic strains after taking antibiotics often delayed gut bacteria and gene expression from returning to their natural "naïve" state.


Even if some of the bacteria in a probiotic managed to survive and propagate in the intestine, there would likely be far too few of them to dramatically alter the overall composition of one's internal ecosystem. Whereas the human gut contains tens of trillions of bacteria, there are only between 100 million and a few hundred billion bacteria in a typical serving of yogurt or a microbe-filled pill. Last year a team of scientists at the University of Copenhagen published a review of seven randomized, placebo-controlled trials (the most scientifically rigorous types of studies researchers know how to conduct) investigating whether probiotic supplements—including biscuits, milk-based drinks and capsules—change the diversity of bacteria in fecal samples. Only one study—of 34 healthy volunteers—found a statistically significant change, and there was no indication that it provided a clinical benefit. “A probiotic is still just a drop in a bucket,” says Shira Doron, an infectious disease expert at Tufts Medical Center. “The gut always has orders of magnitude more microbes.”
If you decide to use a probiotic supplement and get clearance from your doctor for doing so, be sure to read the label carefully. You want to be sure that the supplement contains live strains of the bacteria or yeast, and that the life of these strains is guaranteed at the time of use, and not at the time of manufacture. Other points of comparison are the number of bacteria strains and the number of colony-forming units, although this does not necessarily guarantee results.
Yes, they may help. Lebwohl says there are reputable studies that show a link between the use of probiotics and the reduction in IBS symptoms, citing this meta-analysis. It's estimated that 11 percent of the world population complains of symptoms like abdominal cramps, diarrhea, constipation, excessive gas and/or mucus in their stools. While for some the condition can be attributed to certain dietary triggers, others appear to be stress-related, which brings us to the heart of where many claims about the effectiveness of probiotics lie—in the gut-brain axis.
4. Ohnmacht C, Park JH, Cording S, Wing JB, Atarashi K, Obata Y, Gaboriau-Routhiau V, Marques R, Dulauroy S, Fedoseeva M, Busslinger M, Cerf-Bensussan N, Boneca IG, Voehringer D, Hase K, Honda K, Sakaguchi S, Eberl G. The microbiota regulates type 2 immunity through RORγt+ T cells. Science. 2015 Jul 9. pii: aac4263. [Epub ahead of print] PubMed PMID: 26160380.
The bottom line: Stick to trusted whole food sources of probiotics if you don’t know a probiotic supplement brand you trust. “Kimchi, pickled beets, Greek yogurt and sauerkraut are great sources of probiotics. If you don’t like them, throw them into a food you do like, like a smoothie, and add your favorite fruit to help mask the flavor,” Taub-Dix says.
To factor strain-specific benefits into our efficacy score, we referenced the information in these guides. Products were rewarded for containing strains on these lists. Additionally, measured levels of each strain were compared to what is thought to be effective based on these guides, and scores were scaled accordingly. In cases where products did not list strain-specific amounts, or their listed strains were not included in these guides, total measured CFUs were compared to a general effectiveness threshold of 1 billion CFUs cited by research published in the American Journal of Clinical Nutrition11.

The latest two-part research on probiotics was spearheaded by researchers at the Elinav Lab of Immunology at the Weizmann Institute of Science in Israel and colleagues at the Tel Aviv Medical Center. Eran Elinav served as a senior author for both studies along with Eran Segal and his lab of computational biologists who focus on health and disease related to microbiome, nutrition, genetics, and gene regulation. 

Unfortunately, many commercial brands don’t measure up. They are unstable in stomach acid. Quality control measures aren’t intact, including ensuring supplements have been handled correctly and maintain their freshness. Moisture slipping into probiotic supplements can reduce their efficacy. Companies that use bioshield capsules produce higher quality probiotic supplements that are able to endure the stomach acid, releasing their contents within the small intestine, where a more alkaline environment ensures the survival of the bacteria.
Better Health Review named Dr. Ohhira’s Probiotics 12 Plus on its list of the top probiotic supplements on the market. It contains less than a billion active probiotic cells per dosage, but it adds vitamins, minerals and other micronutrients for optimal health. It claims to be 100 percent vegetarian. Better Health Review gives Dr. Ohhira’s Probiotics 12 Plus a rating of 3.5 on a scale of 5.
I didn’t know there was much of a difference between probiotics until I did some research. After realizing the ones I had been getting were probably not doing anything for me, I wanted to invest in a better option. This brand checked all the boxes and was still really affordable! I’ve been taking them for about a week now and I can tell a difference! The first few days I didn’t feel too great but realized it was because this probiotic was actually doing something for me and rebalancing my gut. Now I feel less bloated and all around healthier. I will definitely be getting more!
That's because issues that can be treated with probiotics stem from specific imbalances in the amount of certain bacterial strains, according to Elena Ivanina, M.D., a gastroenterologist at Lenox Hill Hospital. "Therefore, if someone decides to supplement a particular strain of Lactobacillus, but they already have enough of that strain in their gut and their disease does not stem from a lack of Lactobacillus, then they will not have a response." Makes sense, right?
Very few women know that one of the leading causes of infertility, difficulties getting pregnant, and even painful periods stem from thyroid dysfunction. That’s why infertility specialists, obstetricians, and gynecologists alike often order thyroid testing at the first sign of trouble. Poor thyroid function is also linked to joint pain, unplanned weight-loss or obesity and heart problems and thinning skin among many other signs and symptoms.

Many women eat yogurt or insert it into the vagina to treat recurring yeast infections, a "folk" remedy for which medical science offers limited support. Oral and vaginal administration of Lactobacilli may help in the treatment of bacterial vaginosis, although there isn't enough evidence yet to recommend it over conventional approaches. (Vaginosis must be treated because it creates a risk for pregnancy-related complications and pelvic inflammatory disease.) Probiotic treatment of urinary tract infections is under study.


Side effects: Probiotics are considered safe overall for healthy people; short-term side effects may include mild gas and bloating. But risks may be greater in immunocompromised people. And a systematic review in the Annals of Internal Medicine in 2018 found that the reporting of adverse effects is often missing or inadequate. Also in 2018, an editorial in JAMA Internal Medicine by Dr. Pieter Cohen, a well-known critic of the supplements industry, called for the FDA to improve its regulatory standards for probiotics to match those of Canada and the EU.
Most probiotics are like what is already in a person's digestive system. Some probiotics have been used for a very long time throughout history, such as in fermented foods and cultured milk products. These don't appear to cause illness. But more study is needed on the safety of probiotics in young children, the elderly, and people who have weak immune systems.

While past studies have investigated similar questions, they have all used patients' excrement as a proxy for microbe activity in the GI tract. Instead, Elinav, his colleague Eran Segal, (a computational biologist at the Weizmann Institute), and their teams spearheaded by Niv Zmora, Jotham Suez, Gili Zilberman Schapira, and Uria Mor of the Elinav lab collaborated with Zamir Halpern, Chief of Gastroenterology at the Tel Aviv Medical Center to measure gut colonization directly. 

When I polled friends and family about their personal experiences with probiotics, I got a real mixed bag of responses. Some called them a lifesaver and others felt no effects whatsoever. I put the anecdotes aside and talked to Ben Lebwohl, gastroenterologist and director of clinical research at Columbia University’s Celiac Disease Center, to get the straight poop on whether probiotics are miracle or myth.

Historically, people had plenty of probiotics in their diets from eating fresh foods from good soil and by fermenting foods to keep them from spoiling. Over a century ago, the Russian Nobel Prize winner Elie Metchnikoff theorized that “health could be enhanced and senility delayed by manipulating the intestinal microbiome with host-friendly bacteria found in yogurt.” Metchnikoff was ahead of his time with his view of probiotics benefits, but he also was aware that most citizens had regular access to probiotic foods.
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