One of the controversies around milk drinking and human health is its role in healthy bones. Most focus is put on the calcium in milk, but epidemiological studies on the relation between calcium intake and bone health show mixed results. In this blog, I will give my perspective on this topic.
As mentioned in an earlier blog (link), milk products are an important source of nutrients. Dairy contributes proportionally more protein, calcium, magnesium, phosphorus, potassium, zinc, selenium, and several B vitamins than calories to the diet. In developed countries especially, dairy products contribute significantly to the intake of protein and these essential nutrients.
Several of these nutrients have been linked to healthy bones, especially calcium. However, nutrients do not work in isolation and beneficial health effects will not result if the intake of one or more of a set of nutrients is suboptimal. Bone health is a good example of this, because it depends on the adequate intake of several essential nutrients, including protein, calcium, phosphorus and vitamin D.
But healthy bones require more than the nutrients mentioned. Healthy bones also need sufficient exercise. Both for children (building bone mass) and in adults (loosing bone mass), a combination of the right set of nutrients and sufficient exercise is required.
This synergistic effect of several nutrients with sufficient exercise is, in my opinion, a possible explanation for the unclear results from nutritional studies on bone health. Most studies focus on single nutrients, and don’t take the whole set of nutrients plus exercise into account. It is also important to realize that not all nutrients from different food products are equally bioavailable to the body, with dairy products generally having a high bioavailability of its nutrients.
In conclusion, simply looking at calcium intake is an incorrect way to estimate the effect of dairy intake on healthy bones, as it ignores the important synergy between several nutrients and exercise, where dairy products do not only provide calcium but the whole set of nutrients. Therefore, dairy consumption can contribute to healthy bones, but needs to be complemented by exercise.
Kasper Hettinga, April 2018