New review on milk and bone health

Milk is a natural source of protein, vitamin B2 and B12, calcium, phosphorus, potassium and iodine. Protein, calcium and phosphorus are among the many nutrients that contribute to bone maintenance. A review by Van den Heuvel and Steijns (2018) provides a scientific overview on the topic of milk and bone health.

Summary | Van den Heuvel and Steijns (2018) conclude that dairy products, with or without vitamin D enrichment, may have a positive effect on bone mineralization in children and adults with low baseline calcium intake. However, there are several areas that require more research such as dairy consumption in children and bone health later in life; research in other population groups besides women, Western and Chinese; and role of other dairy products besides milk in bone health.

Bones consist of a protein matrix filled with calcium phosphate and other minerals such as sodium, magnesium, potassium and zinc. Bone is a living tissue. It is continuously broken down and rebuild. It takes 30 years to reach peak bone mass. Despite the fact that 60-80% of peak bone mass is hereditary, other factors such as movement, vitamin D intake and a healthy diet also plays a part in the development and maintenance of bone mass. Milk naturally contains nutrients such as protein, calcium and phosphorus. Besides those nutrients, cheese also naturally provides vitamin K and zinc. These are nutrients that play a role in the maintenance of bone mass. However, In the case of calcium, a global comparison showed that calcium intake varies worldwide, and in many countries in Asia it is lower than 500 mg/day.

Figure: Bone mass during life (NIH 2004, Ortho Info 2012)

Review by Van den Heuvel and Steijns (2018)

Van den Heuvel and Steijns (2018) included only systematic reviews and meta-analyses on randomised controlled trials in the case of bone mineralisation or prospective studies in the case of fracture risk, or in other words studies of high quality listed in Scopus and/or Pubmed. Only studies in the English language were included.

The inclusion criterium for the study population in this review was healthy subjects above the age of 1 year. The minimal study duration of an intervention directing towards a higher bone mass density (BMD) or bone mineral content (BMC) was 2 years for studies involving adults and 1 year for those involving children.

Results of the review

A total of 6 meta-analyses and 2 systematic reviews examining 33 RCTs, 25 prospective studies and 3 individual prospective studies were included in Van den Heuvel and Steijns’ (2018) review.

Dairy and bone health in children and adolescents

The review showed that consumption of plain dairy and dairy fortified with calcium and/or vitamin D raised BMC by 45-50 g over the duration of one year. This finding was reflected in two meta-analyses involving Chinese and Western girls with a calcium intake of less than 750 mg/day. The increase in BMC associated with dairy intake is comparable to the effect of exercise. With exercise, BMC increases by 117 grams over a duration of 2 years, surrounding the formation of the peak bone mass in physically active boys and girls (Bailey et al, 1999).

Dairy and bone health in adults

Mother pours milk into glass for daughter at kitchen table

According to the review, a meta-analysis showed that the BMD of Western women increases by 0.7-1.8% in 2 years when they consumed more dairy, regardless of enrichment with vitamin D. The BMD was measured at various sites in the body, including the lumbar and femur. This increase in BMD is approximately 1/5 of the effect that can be achieved with the use of pharmacotherapy. Nevertheless, the increase in BMD due to dairy consumption appears significant when compared with BMD decrease due to ageing, which is around 1-2% per year. For lumbar spine BMD, based on a few comparisons, the increase seems to be independent of baseline dietary calcium intake. However, this could not be investigated for other BMD sites and further studies are needed.

Dairy products versus calcium supplements

There is potential for research on this topic as the review by Van den Heuvel and Steijns (2018) found only 1 meta-analysis that directly compares the efficacy of dairy products with calcium supplements. The single meta-analysis suggests that both are similarly effective for BMD. However, it is important to note that patient compliance rates for calcium plus vitamin D supplements are as low as 2-in-10 patients.

Key points

  • Milk is a natural source of protein, vitamin B2 and B12, calcium, phosphorus, potassium and iodine.
  • Calcium, vitamin D and protein contribute to the maintenance of bones in adult life (International Osteoporosis Foundation, 2011).
  • Physical activity can increase peak bone mass by 117 gram over a period of 2 years (Bailey et al, 1999). Similarly, drinking milk can increase bone mineral content (BMC) in children by 90-100 gram over 2 years (Van den Heuvel et al, 2018). This was found in a total number of 19 randomized control trials, of which 14 studies showed a beneficial effect while 5 were neutral.
  • A small increase of BMC in children can have a significant impact on bone health; a 10% increase in peak bone mass provides a 50% reduction in the risk of fracture later in life (Bonjour et al, 2009).