Dairy Products and Their Role in Human Health
Teresa Trotta, Francesca Posa, Giorgio Mori and Chiara Porro
Department of Clinical and Experimental Medicine, University of Foggia, Italy
Milk, since birth, is an omnipresent food in human diet. It has an unquestionable nutritional richness, contains important vitamins, essential minerals and high biological value proteins. Milk and dairy products are frequently included as important elements in a healthy and balanced diet, even if several controversial recent hypotheses attribute to their consumption a negative influence on human health. This section analyzes the effect of dairy products consumption on diseases such as cancer, metabolic syndrome, and osteoporosis, and considers lactose intolerance and milk allergy as adverse reactions to milk ingestion.
Dairy Products and Cancer
Cancer has a complex and multifactorial aetiology. Genetics and environmental factors both contribute to its development; thus, there is no available evidence to prove the effect of a single food and/or nutrient on its origin and development. Lipids are an important energy source that would potentially increase cancer cell proliferation, and excessive fat consumption may affect the production of hormones, which can be involved in prostate and breast cancer development (Pereira 2014). Although a high intake of dietary fat has been implicated in the development of some cancers, including colon, breast, and prostate cancer, it is not clear if milk consumption increases or decreases the risk for cancer. Some milk components can play a protective role in carcinogenesis, whereas others can promote this phenomenon and increase cancer risk.
Control and case-control studies have shown inverse associations or no effect of moderate milk consumption in breast (Bessaoud et al., 2008; Moorman and Terry 2004; Zhang et al., 2011), prostate (Huncharek et al., 2008), bladder (Li et al., 2011) and colorectal (Aune et al., 2012; Murphy et al., 2013) cancers. However, this is not free from controversy. For example, in breast cancer, on the one hand, a diet high in saturated fats, the probable presence of pesticides and growth factors, such as IGF-1 (that can promote cancer cell growth) increase the cancer risk (Moorman and Terry 2004). On the other hand, some components in dairy products, such as calcium, vitamin D, rumenic acid, butyric acid, branched chain fatty acids, and whey protein may play a role in cancer prevention (Moorman and Terry 2004; Parodi 2005).
Advances in Dairy Products, First Edition.
Edited by Francesco Conto, Matteo A. Del Nobile, Michele Faccia, Angelo V. Zambrini, and Amalia Conte.
© 2018 John Wiley & Sons Ltd. Published 2018 by John Wiley & Sons Ltd.
Similarly, prostate cancer development is probably influenced by various mechanisms that include metabolites of branched-chain fatty acids and oestrogens that may be carcinogenic, calcium suppressed production of calcitriol (1,25-dihydroxyvitamin D), thus increasing cell proliferation in the prostate and increasing blood levels of IGF-1, fat, SFA41 (Parodi 2009). Another hypothesis is that excessive calcium intake impairs the synthesis of vitamin D and possibly promotes vitamin D receptor gene polymorphisms, which suppress its modulating role in prostate cell tumor growth and development (Arai et al., 1997; Kricker and Armstrong 2006; McKay et al., 2009).
Regarding colorectal cancer, epidemiologic evidence suggests that moderate milk consumption is associated with lower cancer risk (Murphy et al., 2013), and calcium, vitamin D, and folate are the milk components most frequently associated with this protective effect. These three micronutrients play a crucial role in regulating cell proliferation affecting the carcinogenesis process (Lamprecht and Lipkin 2003). Calcium in milk may play a protective role in colon cancer, given that intracellular calcium directly influences cell growth and apoptosis (Wiseman 2008). It is important to note folate's role in DNA methylation, which is the possible interplay between nutrient and cancer genetic aetiology (Duthie 2011). In fact, folate intake has been inversely associated with colorectal cancer in experimental and epidemiologic studies (Eussen et al., 2010; Kennedy et al., 2011). However, some dairy products, such as certain cheeses and creams, also have a high-fat content that potentially could increase colorectal cancer risk by increasing bile acid levels in the colon. Epidemiological studies of dairy products and colorectal cancer risk have provided mixed results. Some cohort studies have reported inverse associations between intake of total dairy products, milk and/or yogurt, and colorectal cancer risk, while other studies found no association (Aune et al., 2012).
Most (Bhattacharya et al., 2006; De Noni et al., 2009; McGann et al., 1983), but not all (Singh et al., 1989), studies examining calcium intake have suggested an inverse association with pancreatic cancer risk. Genkinger et al. (2014), in an effort to investigate the association of dairy product intake, calcium, and vitamin D with pancreatic cancer risk in a large international consortium of 14 prospective cohorts, do not support the hypothesis that their consumption is associated with pancreatic cancer risk.
Considering these data, it is possible that the complex aetiology of cancer does not allow a clear and evident conclusion about a positive or negative role of milk consumption in cancer risk; diets high in calcium are a probable cause of prostate cancer, but there is limited evidence suggesting that excessive consumption of milk and dairy products is a cause of prostate cancer. Furthermore, high milk intake can also increase the risk for breast and prostate cancers due to the influence of fat in androgens and estrogens, as well as to the increased energy availability, which would facilitate cancer development. However, there is no conclusive evidence for a relationship between milk and dairy products and cancer due to insufficient data. These associations are not common in all cancer forms—moderate milk consumption, regardless of fat content, has a protective effect in colorectal cancer (Pereira 2014). Lampe (2011) reported an inverse association between milk intake and risk of colorectal cancer and a positive association between diets high in calcium and risk of prostate cancer, and Aune et al. (2012) reported that milk and total dairy products, but not cheese or other dairy products, are associated with a reduction in colorectal cancer risk. Currently, the research does not support a strong link between cancer risk and intake of milk and dairy products, but healthy, well balanced diet is recommended.