Kefir, sometimes called milk kefir, is a fermented beverage made from milk inoculated with kefir grains, otherwise considered a traditional yeast-like starter.1 This beverage can be found in cultures around the world, but it is believed to have originated in Russia.2 Properly fermented kefir yields a thick, slightly sour liquid with a mild sparkle from the small amount of alcohol.

Kefir was first documented as a health supplement in the 1880s, but in the last decade it has gained worldwide attention. Kefir is generally included in the category of natural probiotics, with the added benefits of vitamins, minerals, and some proteins.

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Kefir can be made from most any kind of milk product, including cow’s milk, soy, or coconut milk. The difference in the final product is seen in the variation of types of bacteria contained in the starter, or grains. In traditional cultures, these starters were handed around the community as needed, much like some popular bread recipes. For those wishing to grow their own kefir, usually a starter culture can be purchased from a health food store. From there, follow the simple directions. Because gut flora play a key role in immunity, proponents of alternative therapies believe that products such as kefir have tremendous potential for promoting health and preventing disease.

Scientific data

One common malady that kefir is useful in managing is lactose intolerance. Because of the fermentation process, lactose in the milk is broken down, leaving a product that is basically lactose free. In a randomized study, 15 healthy adults with diagnosed lactose intolerance were given premeasured milk, yogurt, or kefir following a 12-hour fast.3 Outcome measurements were breath hydrogen excretion and subjective symptoms. Compared with the milk group, those who drank kefir showed a 250% reduction in both exhaled hydrogen level and subjective symptoms, which was similar to results in the plain yogurt group.

Another disease that causes significant health impact is rotavirus. In an in vitro study, kefir was introduced into an isolated strain of rotavirus to determine the degree to which it could inhibit the rotavirus activity.4 After the incubation period, the reduction in human rotavirus averaged 72% compared with no treatment.

Researchers also examined the effect of adding kefir to standard triple therapy used to treat Helicobacter pylori.5 They randomly assigned 82 patients with symptomatic H. pylori infection confirmed by urea breath testing. The treatment group was given the usual triple therapy along with 1 cup of kefir daily, while the control group received triple therapy and a milk placebo. Because H. pylori tends to either recur or resist therapy, all participants were retested for infection after 45 days. The kefir group achieved a 50% higher eradication rate than those in the placebo group. 

Cost, dose, and how supplied

Commercially prepared kefir is usually purchased in containers very similar to a quart of milk. Kefir is not inexpensive, averaging $5 to $20 per quart in retail outlets. As one would imagine, home-cultured kefir costs about one-half that amount, depending on the type of milk used and the kefir grains purchased. 

As far as dosing, there are no actual dose recommendations. Kefir may by consumed in whatever quantity preferred. The literature has a wide range of examples from 1 tablespoon to ½ cup per day, but to date, there has been no attempt to standardize the dose because the mixture itself is not consistent. 

In a laboratory study using mice, researchers compared fermented milk products with different added concentrations of the prebiotic inulin.6 Subsequently, they evaluated the level of active probiotics in the gut correlated with the concentration of inulin. It was found that the higher the level of inulin, the more robust the probiotic activity. Although this obviously would need to be verified in human trials, it would seem that probiotics in actual functional foods such as kefir are more viable and active than those in capsule or another supplement form. Anecdotal information on several websites estimates that probiotics consumed in actual foods are “hundreds of times” more effective than supplements, but there are no studies to validate this claim.

Safety, interactions

Commercially prepared kefir is considered safe, mainly as a result of the pasteurization process that is required for dairy products. The downside of this is that many feel the best probiotics are also killed during this process, even if supplements are added after the heating of the product Home preparation of kefir opens the door to many questions of safety, because individual kitchens and products cannot be controlled. Milk products and kefir starters can contain any number of harmful agents.

Interactions to the kefir itself would more likely be to the base milk product than to the probiotic component. Many medications, especially antibiotics, are not appropriately absorbed when taken in conjunction with milk products. Otherwise, no interactions have been noted.

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Kefir is yet another natural product that has become popular in recent years but has been a staple in many cultures for centuries. Most likely born out of necessity because of the lack of any method of refrigeration, kefir is now in the spotlight of the world of alternative medicine. Not unlike many alternative therapies, the actual scientific data from controlled human trials are nearly nonexistent. However, because the safety data are relatively benign, and some laboratory studies seem to indicate the superiority of probiotics in a base such as kefir compared with capsule supplements, kefir is an acceptable choice and one that can be reliably approved in primary care practices. 


  1. Otles S, Cagindi O. Kefir: a probiotic dairy-composition, nutritional and therapeutic aspects. Pakistan J Nutrition. 2003;2:54-59.
  2. Editors of Webster’s New World Dictionaries. Webster’s New World Dictionary. 4th ed. Kefir. Boston, MA: Houghton Mifflin Harcourt; 2012.
  3. Hertzler SR, Clancy SM. Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. J Am Diet Assoc. 2003;103:582-587.
  4. Song J-O, Kim T-J, Kim Y-H. Inhibitory effect on rotavirus by exopolysaccharides extracted from kefir [in Korean]. Korean J Food Sci Ani Resour. 2007;27:538-542.
  5. Bekar O, Yilmaz Y, Gulten M. Kefir improves the efficacy and tolerability of triple therapy in eradicating Helicobacter pylori. J Med Food. 2011;14:344-347.
  6. Aghajani A, Pourahmad R. Effect of lactulose and inulin on physicochemical and microbial properties of synbiotic yogurt. Ann Biol Res. 2012;3:5692-5696.