Susan A. New, BA, MSc, PhD

Disclosures

September 09, 2003

Question

If the results concerning calcium supplementation are controversial, are milk and dairy products important for bone health?

Response From the Expert

Susan A. New, BA, MSc, PhD, RPHNutr
Center for Nutrition & Food Safety, School of Biomedical & Life Sciences, University of Surrey, Guildford, Surrey, United Kingdom

 

Individuals consume, on an average Western diet, approximately half a pint of milk per day, with whole milk representing about 33.4% of the household milk market and semi-skimmed milk representing 7.6% of milk sales. Milk and dairy products provide approximately 19% of the daily intake of protein and approximately 8.5% of the total amount of fat. Milk and milk products provide over 50% of the total calcium in the diet as well as a number of other key nutrients, including phosphorus, magnesium, and zinc, all of which have been shown to be important to bone health. As noted by Heaney,[1] dairy products are complex, containing many essential nutrients. Thus their effects on bone health are likely "more than can be accounted for by any single constituent and the totality of their effects may be more than the sum of parts."

A number of retrospective studies have shown a link between low milk consumption during the childhood and adolescence and lower bone mineral density (BMD) in young women, premenopausal women, and older postmenopausal women. In a recent study of Chinese adolescent girls aged 12-14 years (N = 649), milk intake was found to be positively associated with distal radius and ulna bone mass (P < .05), with milk accounting for 3.2% of the variation in BMD.[2]

Few studies have used food sources of calcium (particularly dairy products) as the supplementary vehicle to investigate the complexity between calcium and peak bone mass attainment. However, of those studies that have been published, the results demonstrate a clear positive effect on bone mineral. In the milk supplementation trial by Cadogan and colleagues,[3] teenage girls who consumed a 300-mL milk supplement every day for 18 months had significant increases in total body BMD (9.6% vs 8.5%) and total body bone mineral content (BMC) (27% vs 24%) compared with the control group. Insulin-like growth factor I levels were found to be higher in the milk group, thus raising the possibility of periosteal bone apposition stimulation, which would result in a slightly larger skeletal envelope.

In the prospective, randomised, placebo-controlled, double-blind study published by Bonjour and associates,[4] the effects of calcium-fortified foods on bone mass at different skeletal sites were investigated in a cohort of prepubertal girls aged 7-9 years. The foods were enriched with calcium salts from milk extract (in the form of phosphate salts). Not only were benefits seen in bone mass, but differences were also found in height between the supplemented and unsupplemented groups. Effects were greatest in girls with a spontaneous intake below the median. For example, an increase in calcium intake from 711 ± 19 mg/d to 1441 ± 34 mg/d (ie, a mean supplementary intake of 730 mg/d) resulted in gains in areal BMD (aBMD), BMC, and bone area in comparison to the placebo group by 58%, 23%, and 15% respectively. Three years after discontinuation of the intervention, the differences in the gain in aBMD and in the size of some bones were still detectable, and after 3.5 years this difference remained.[5]

Milk-supplementation studies have demonstrated a positive relationship with bone health in pre- and postmenopausal women. Heaney and colleagues[6] found favorable effects on markers of bone metabolism in postmenopausal women following supplementation with dairy products. In the most recent study by Lau and coworkers,[7] the effect of milk supplementation on postmenopausal bone loss in Chinese women accustomed to a low calcium diet was investigated. A total of 200 Chinese women aged 55-59 years were randomly assigned to receive 50 g of milk powder (containing 800 mg of calcium) per day or were assigned to a control group. Subjects were recruited through notices posted in community centers. The results showed that the milk-supplementation group had a significantly reduced height loss as well as reduced BMD loss at the 3 sites measured. For example, the mean percentage change in height was -0.1 ± 0.2 cm in the milk group compared with -0.2 ± 0.1 cm in the control group. The mean percentage change in hip BMD was -0.06% ± 0.22% for the milk group compared with -0.88 ± 0.26% in the control group. Serum PTH was also found to be lower and serum 25 (OH) D significantly higher in the milk group compared with the control group at 12 months. The authors concluded that supplementing the diet of postmenopausal Chinese women with a milk powder that is rich in calcium significantly retards bone loss.

Only a few studies have been published concerning milk consumption and fracture risk. Cumming and Klineberg[8] found that a higher level of consumption of dairy products at 20 years of age was associated with an increased risk of hip fracture in both elderly men and women (aged 65 years and older) and similar results have been found in the USA Nurse's Health Study. However, Johnell and colleagues[9] found that low milk intake was a significant risk factor for fracture in a large study of European women (mean age, 78.1 years) and a low intake of milk and cheese has also been found to be associated with an increased risk of fracture in elderly men.[10] Other studies have reported a negative effect of milk and dairy products on fracture risk.

In summing up the evidence for milk and dairy products, milk is an important ingredient for optimum bone health in both younger and older population groups.

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.

processing....