Fermented dairy products contain adequate levels of certain

Fermented dairy products contain adequate levels of certain live and active cultures, namely probiotics that aid to improve the balance of “beneficial” versus “undesirable” bacteria in the intestinal tract. Several researches on fermented dairy products showed their effect on the immune system, as well as promoting intestinal health. The impact of consuming fermented products such as yogurt on improving the immunity function in body against carcinogens and harmful toxins is being studied. In order to find out the effect of milk and dairy products intake in reducing the risk of diseases, clinical investigations have been done on diseases such as GI system diseases, cardiovascular system diseases, musculoskeletal system diseases, urogenital system diseases, immune system diseases, allergy, nervous system diseases, cognitive system diseases, weight control, obesity, aging and dental health [92]. Such products as yogurt play a potential role in decreasing intestinal disorders and chronic diseases. According to a recent study, several non-nutrient components in yogurt such as sphingolipids, conjugated linoleic GW 610 and butyric acid may play a role as anti-cancer agents [13]. The positive effect of probiotics on food allergies in children is another promising area of study. Recent studies in infants have revealed that probiotics not only alter the response to potentially harmful antigens (substances that induce allergies), but also reduce their allergenic potential [14]. Fermented dairy products are a good instance of functional foods. Many scientific studies confirm yogurt and other fermented diary products’ functional role which are increasingly advancing the immune system and preventing diseases. Fermented dairy products are good, and in some cases excellent, sources of nutrients namely calcium, protein and potassium [15].
Fortification with vitamins Vitamins are compounds which play a role as cofactors in the body. Fermented milk products such as yogurt can be thought as vitamin sources. However, due to the ability of some starters to synthesize vitamin B that is necessary for their growth, there are different vitamin contents in yogurts. Thus, yogurt and fermented milk products which are produced by strains, may have different vitamins according to the starter that is used [10]. Furthermore, evaluation of vitamins is more difficult since processes like heat treatment, incubation time, temperature and storage conditions change the vitamins content in yogurt [17]. The approximate vitamin content of full fat and nonfat yogurt, and comparison of whole milk and skimmed milk are shown in Table 1[16]. Vitamin D is vital for appropriate skeletal development which plays a fundamental role in regulating serum calcium and phosphorus concentrations in the body. Due to the photosynthesis of vitamin D in the skin after exposure to solar UV radiation, it is not included in the category of essential nutrient of the body [18]. On the other hand, at latitudes above 40°N or below 40°S and for several months of the year, no photosynthesized vitamin D is produced in the skin; thus, in order to prevent deficiency, supplementation of vitamin D is required [19,20]. Furthermore, the amount of vitamin D produced in the skin as a result of exposure to the sun is limited by application of sunscreen [21]. Diseases such as childhood rickets, osteoporosis and osteomalacia are influenced by vitamin D deficiency. It has also been shown that the increase in the risk of developing cancers, osteoporotic fractures, and autoimmune diseases have a direct relationship with vitamin D deficiency [22]. Since vitamin D is a hormone, its receptor, which belongs to the family of steroid/thyroid hormone nuclear receptors, mediate its genomic mechanism of action. Antiproliferative, differentiative and apoptotic effects of this vitamin were observed on prostate cancer cells in vitro [23–25]. Concerning the epidemiological studies, vitamin D has negative effects on breast [26] and colon cancers [27]. Also, vitamin D deficiency might result in type I diabetes, hypertension, multiple sclerosis and some other cancers [28]. Several researches have been conducted on the stability of vitamin D in milk and other dairy products [29–33], which all have claimed that vitamin D is stable during processing and storage. There are not adequate amount of vitamins A and C in low fat dairy products which are not fortified. Usually, low fat milk and other dairy products are enriched with vitamin A but not with vitamin C. Fortification of dairy products with vitamins A and C leads to improvement in their nutritive quality and consequently, increases their acceptability [34,35].