The development and maintenance of the immune system depend largely on healthy gut microbiota. As fermented and probiotic milk products are a source of beneficial live microorganisms that can improve gut microbiota, a number of studies have investigated the role of these products in immune regulation. To date, the available evidence suggests that fermented milk products may enhance immune functions.
- Fermented milk products such as yogurt may promote cellular immune functions.
- Both regular and probiotic yogurt appear to have favourable effects on immune function.
A randomized controlled trial by Meyer et al. evaluated whether yogurt consumption had stimulating effects on the immune system. Thirty-three healthy women aged 22 to 29 years were randomized to either a conventional or a probiotic yogurt. The subjects consumed 100 g per day of the respective products for 2 weeks, and the amount was increased to 200 g for the subsequent 2 weeks. It was found that both products enhanced cellular immune functions, but there was no significant difference between them.1
In another randomized controlled trial, the effect of the dietary deprivation of fermented foods on the immune system was assessed. The study consisted of 20 healthy adult volunteers aged 23 to 43 years who regularly consumed yogurt and/or cheese (at least 5 servings per week) and other fermented products (at least 3 servings per week). They were instructed not to consume any fermented products for 2 weeks. Following this restriction, the participants were randomized to the daily consumption of 200 mL of either regular or probiotic yogurt for 2 weeks.2
- The deprivation of fermented foods was associated with a fall in innate immune response.
- Both the regular and probiotic yogurt counteracted the adverse immunological effect.
- The probiotic yogurt was more effective than the regular yogurt at counteracting the fall in immune response.
Marcos et al. conducted a prospective randomized controlled trial to investigate the effect of milk fermented with yogurt cultures plus Lactobacillus casei on the immune system of individuals under academic examination stress. The participants were 155 healthy university students aged 18 to 23 years. For 6 weeks, they were assigned to either 1 daily glass of semi-skimmed milk or 2 daily servings of 100 mL of the fermented milk product. The results indicated that the fermented milk product may modulate immune response among individuals under academic examination stress.3
In addition to human studies, several animal models have been used to examine the immunomodulatory effect of milk products. In a 2012 study, it was observed that a cheese-containing diet modulated immune responses in mice.4 Another study suggested that a fermented milk product with 2 probiotics and a prebiotic may have a beneficial effect on the humoral and cell-mediated immunity of host animals.5
Fermented milk products contain large quantities of beneficial bacteria such as lactic acid bacteria, which may enhance both innate and adaptive immunity. The immunomodulatory activity of lactic acid bacteria includes the activation of the systemic and secretory immune response via the coordination of interactions between the microbiota, epithelial cells and immune cells.6
Milk and milk products contain bioactive peptides that have been shown to increase the activity of immune system cells. Evidence suggests that these peptides assist in the proliferation of lymphocytes, the functioning of natural killer cells, the synthesis of antibodies and the production of cytokines.7 It has been demonstrated that both conventional and probiotic yogurt may stimulate cytokine production and promote higher alertness of the immune system.8
Lactoferrin, an iron-binding glycoprotein found in milk and milk products, is an immune modulator and has antimicrobial and antioxidant properties. It influences innate and adaptive immunity by modulating the migration, maturation and functions of immune cells.9
Evidence on the immunological properties of milk products comes principally from studies on fermented milk products. These studies indicate that both conventional and probiotic fermented milk products such as yogurt may strengthen the immune system.
Further research from randomized controlled trials is needed to determine whether conventional and probiotic fermented milk products have different effects. Additional studies are also needed to investigate the potential benefits of different types of milk products.
- Meyer AL et al. Daily intake of probiotic as well as conventional yogurt has a stimulating effect on cellular immunity in young healthy women. Ann Nutr Metab 2006;50(3):282-9.
- Olivares M et al. Dietary deprivation of fermented foods causes a fall in innate immune response. Lactic acid bacteria can counteract the immunological effect of this deprivation. J Dairy Res 2006;73(4):492-8.
- Marcos A et al. The effect of milk fermented by yogurt cultures plus Lactobacillus casei DN-114001 on the immune response of subjects under academic examination stress. Eur J Nutr 2004;43(6):381-9.
- Hosoya T et al. A cheese-containing diet modulates immune responses and alleviates dextran sodium sulfate-induced colitis in mice. J Dairy Sci 2012;95(6):2810-8.
- Wang S et al. Fermented milk supplemented with probiotics and prebiotics can effectively alter the intestinal microbiota and immunity of host animals. J Dairy Sci 2012;95(9):4813-22.
- Ebringer L et al. Beneficial health effects of milk and fermented dairy products--review. Folia Microbiol (Praha) 2008;53(5):378-94.
- Meyer AL et al. Probiotic, as well as conventional yogurt, can enhance the stimulated production of proinflammatory cytokines. J Hum Nutr Diet 2007;20(6):590-8.
- Tsai YT et al. The immunomodulatory effects of lactic acid bacteria for improving immune functions and benefits. Appl Microbiol Biotechnol 2012;96(4):853-62.
- Legrand D and Mazurier J. A critical review of the roles of host lactoferrin in immunity. Biometals 2010;23(3):365-76.