New review: milk and health

Milk products are included in dietary recommendations all over the world and are a regular part of many people’s diets. Scientists therefore reviewed existing research on milk and dairy consumption and the different health outcomes, including cardiovascular health, bone health and weight management.

In a varied diet, milk and other dairy products contribute to the intake of various nutrients, such as protein and calcium. For that reason, milk and other dairy products are included in dietary recommendations all over the world. Research shows that milk and other dairy products contribute to healthy bones and weight management. There is no link to unfavourable outcomes with respect to cardiovascular health.

Milk is included in dietary recommendations worldwide and is part of a healthy and varied diet. For example, milk and other dairy products naturally provide many nutrients that we need on a daily basis, such as protein and calcium. However, some people question whether milk is good for us. Recently, two articles were published about epidemiological studies and Randomised Controlled Trials, which analysed the relationship between milk and other dairy products and health (1-2). These were reviewed by Lamarche et al (2016) and Thorning et al (2016). These reviews are discussed in more detail below, with a specific focus on cardiovascular health, bone health and weight management.

Cardiovascular health

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Research shows no connection between the consumption of milk and other dairy products and unfavourable outcomes with respect to cardiovascular health (1-2). This is the conclusion of the reviews by Lamarche et al (2016) and Thorning et al (2016). In these analyses, a distinction is made between various clinical outcomes related to cardiovascular health: coronary heart disease, stroke, type 2 diabetes and cardiovascular disorders as a whole. In November 2016, a review was published which explains in detail the latest scientific knowledge regarding the consumption of various dairy products and cardiovascular health.

Background

The primary treatment of cardiovascular disorders includes lowering LDL cholesterol concentrations and blood pressure. Research shows that saturated fatty acids increase LDL cholesterol in the blood compared to carbohydrates and monounsaturated and polyunsaturated fatty acids. For that reason, the general recommendation is to replace saturated fatty acids with polyunsaturated fatty acids. However, people do not eat separate macronutrients, but foodstuffs that each have their own specific macronutrients and micronutrients profiles. This may explain why milk products have a neutral effect on cardiovascular health, contrary to the expectations based on the relationship between all saturated fat and LDL cholesterol. In fact, a distinction can be made between larger and smaller LDL cholesterol particles in which the smaller particles are more unfavourable than the larger particles. Small dense LDL particles (sdLDL-p) are rich in triglycerides. They have less affinity with the LDL receptor, attach themselves more readily to the vascular wall and are more sensitive to oxidation than the larger particles. These properties are less favourable for maintaining a healthy cardiovascular system. It seems that some saturated fatty acids (e.g. C14 and C16) in dairy products in particular have an effect on the larger LDL cholesterol particles. Furthermore, milk, yoghurt, soft curd cheese and cheese also contain protein, calcium and other minerals. Thus milk naturally contains calcium as well as the minerals phosphorus and potassium. These nutrients can also explain why milk and other dairy products have a neutral effect on cardiovascular health. (1-2) More research is required to unravel this complex connection and clarify its clinical relevance.

Mozzafarian (2016) therefore advises putting more emphasis on foodstuffs and diets and less on separate nutrients in dietary recommendations. He advises focusing on the quality of the fats rather than on reducing fat consumption. According to Mozzafarian, in practice this means: eating less processed meat and fewer foodstuffs containing relatively high levels of refined carbohydrates and salt. Recommended foods are yoghurt, fruit, vegetables, nuts, legumes, fish, wholemeal products and vegetable oils. Eggs, poultry, milk and cheese also fit into this diet. (3).

Bone health

Protein, calcium, phosphorus, magnesium, zinc and vitamins K and D contribute to the build-up and maintenance of bone mass. Within the entire diet, milk and dairy products are by nature important suppliers of these nutrients, with the exception of vitamin D in non-enriched milk products and vitamin K2, which is not found in milk but which is found in fermented milk and dairy products (particularly Dutch Gouda cheese). Because of this composition of nutrients, it is assumed that milk and other dairy products in a varied diet contribute to bone health. The two reviews by Lamarche et al (2016) and Thorning et al (2016)refer to various types of research. The final conclusion is that milk and other dairy products do contribute to bone density and consequently bone health, particularly in children and adults. More cohort studies and randomised studies are required to draw scientifically justified conclusions about the risk of fractures.

Weight management

Milk products are an important source of protein. Protein plays an important role in weight management, probably because of the higher saturating effect of protein compared to carbohydrates and fats. In Thorning et al (2016) a number of studies investigating the effect of the consumption of dairy on weight are mentioned. In children, there is no relation between dairy intake and a higher fat mass, whilst one meta-analysis shows that eating dairy products contributes to weight management. Energy restriction studies with adults show that dairy and milk products in diets help improve the composition of the body and the relationship between fatty and fat-free mass in the short term. Longer term studies without energy restriction show that the consumption of milk and other dairy products in the overall diet has a neutral effect on weight.

Research questions

Both studies conclude that there is a good reason why milk and other dairy products are included in dietary recommendations all over the world. The consumption of milk and other dairy products boosts the intake of various nutrients that have a favourable influence on health. Future research will have to provide more clarity about the differences between fullfat and semi-skimmed dairy products. In most research, fullfat dairy includes both fullfat milk (3-4% fat) and Dutch type cheese (40-45% fat) and are considered together. However, the fat content in these products differs considerably. In order to be able to better study the health effects of milk, the various types of milk must be compared with each other based on fat content. Fermented milk, for example buttermilk, may have a different effect too.