Milk and dairy products: are they really good for health?

Is milk really good for health, or should we limit its consumption? This dilemma continues to arise even after many studies were published on the subject, but with conflicting results. If specific adverse reactions to milk components are excluded, typically lactose, it has never been clarified whether the consumption of milk, particularly in adulthood, can be a source of negative health effects.

In United States, the Department of Health and Human Services and the U.S. Department of Agriculture (USDA) have published dietary guidelines for the period 2015 – 2020. The document notes that the consumption of dairy products, for most age groups, is far below the recommendations. In particular, the average intake of dairy products for children aged between 1 and 3 seems to meet the recommended quantities, while all other age groups assume lower quantities.

In Europe, according to USDA data, annual milk consumption fell from 71 to 65 liters per capita from 2005 to 2018, while annual cheese consumption over the same period rose from 16 to 18 kg.

The guidelines of the Italian human nutrition society (SINU) recommend the consumption of 2-3 daily portions of milk or yogurt (one portion corresponds to 125 ml of milk or 125 g of yogurt), and 2-3 portions per week of fresh (100 g) or aged (50 g) cheese.

Is Milk Good? A review

A recent review published in the New England Journal of Medicine now tries to clarify the situation, taking into account what has been published on the subject in recent years. The authors of the article are Walter C. Willett, and David S. Ludwig, of the Department of Nutrition at Harvard T.H. Chan School of Public Health.

After some considerations on the composition of cow’s milk, and a direct comparison with breast milk, the authors face one of the most felt problems related to the consumption of dairy products: the prevention of bone fractures. In fact, a substantial consumption of dairy products is often recommended to increase calcium intake and improve bone health, particularly in post-menopausal women.

However, the authors highlight that the countries where the most milk and calcium are consumed are the ones with the highest number of hip fractures.

Other studies, that have shown as levels of calcium assumed were not related to the bone mineral density of the hip, are also mentioned. A meta-analysis shows that the risk of hip fracture is even greater among people who had received calcium supplements, compared to those treated with placebo.

The article also takes into account the consumption of dairy products in children and adolescents, but even in this case the results are rather disappointing. Research in this field seems to show that the relationship between calcium assumed with diet, or as supplements, and bone mineral density follows results obtained in adult. A fairly low threshold for calcium intake seems to emerge, above which a higher intake has a small additional effect on bone mineralization.

Consumption of dairy products, cardiovascular diseases and diabetes

In no field as in the cardiovascular, dairy products have long been demonized. These foods are considered an important source of cholesterol and therefore their consumption is discouraged, not only in patients with cardiovascular diseases, but also in healthy subjects with hypercholesterolemia.

On the other hand, it had been hypothesized that the potassium in milk could help reduce blood pressure, but even in this case the experimental results were unsatisfactory.

Some studies have proposed that cow’s milk could cause type 1 diabetes and, conversely, reduce the risk of developing type 2 diabetes. In the first case, a cross-reactivity between milk proteins and pancreatic islet cells was proposed.

 

Milk consumption and risk of cancer

Among the different negative effects attributed to milk there is also the risk of cancer, in particular breast and prostate cancer. Some associations have also been found between milk consumption and endometrial cancer, particularly in postmenopausal women who did not take hormone replacement therapy.

At the end of the article, the authors propose an interesting chart. Here the risk of mortality from all causes is compared, based on the protein consumed in the diet, of animal or vegetable origin, referring to that of subjects who take proteins derived from dairy products.

In this perspective, by consuming a protein source derived from poultry, fish or unprocessed meat, the risk of mortality is similar to that of people who take proteins derived from dairy products. On the other hand, risk rises with consumption of proteins derived from eggs and processed meat, while it decreases when the protein source are vegetables.

Milk yes or milk no? Let’s sum it up

Almost always happens that the conclusions of the reviews are all too much balanced and, therefore, frustrating. They leave the reader in doubt, without providing clear and precise positions.

This is not the case. Here, the authors outline a fairly clear picture, concluding that recommendations to increase dairy products consumption to three servings per day seem not to be justified.

They propose different policies for adults and children. In the former, if they follow a normal diet, the consumption of dairy products should not be encouraged, because it does not seem to provide benefits, but is potentially capable of damage health. Conversely, in children, if the quality of the diet is low, as can be the case in low-income environments, dairy products can improve the nutritional profile.

As for the need to increase the intake of calcium and vitamin D, the authors suggest preferring food supplements rather than dairy, thus avoiding possible negative effects related to other components of dairy products.

 

This post is also available in: Chinese (Simplified)

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