Milk intake increases bone mineral content through inhibiting bone resorption: Meta-analysis of randomized controlled trials

Formula Milk Supplementation and Bone Acquisition in 4-6 Years Chinese Children: A 12-Month Cluster-Randomized Controlled Trial

Dairy foods are crucial for adequate calcium intake in young children, but scarce data are available on the effects of formula milk on bone acquisition. This cluster-randomized controlled trial investigated the effects of the supplementation of formula milk on bone health in rural children accustomed to a low-calcium diet between September 2021 and September 2022. We recruited 196 healthy children aged 4-6 years from two kindergartens in Huining County, Northwest China. A class-based randomization was used to assign them to receive 60 g of formula milk powder containing 720 mg calcium and 4.5 µg vitamin D or 20-30 g of bread per day for 12 months, respectively. Bone mineral density (BMD) and bone mineral content (BMC) at the left forearm and calcaneus, bone biomarkers, bone-related hormones/growth factors, and body measures were determined at baseline, 6, and 12 months. A total of 174 children completed the trial and were included in the analysis. Compared with the control group, formula milk intervention showed significant extra increments in BMD (3.77% and 6.66%) and BMC (4.55% and 5.76%) at the left forearm at 6th and 12th months post-intervention (all p < 0.001), respectively. Similar trends were observed in BMD (2.83%) and BMC (2.38%) in the left calcaneus at 6 months (p < 0.05). The milk intervention (vs. control) also showed significant changes in the serum concentrations of osteocalcin level (-7.59%, p = 0.012), 25-hydroxy-vitamin-D (+5.54%, p = 0.001), parathyroid hormone concentration (-15.22%, p = 0.003), and insulin-like growth factor 1 (+8.36%, p = 0.014). The percentage increases in height were 0.34%, 0.45%, and 0.42% higher in the milk group than in the control group after 3-, 6-, and 9-month intervention, respectively (p < 0.05). In summary, formula milk supplementation enhances bone acquisition at the left forearm in young Chinese children.

Milk Consumption and Bone Mineral Density in Adults: Using Data from the Korea National Health and Nutrition Examination Survey 2008-2011

Background

Milk consumption is associated with bone mineral density (BMD), but reports are limited in terms of participant age, sex, and number of study subjects. We investigated the association between milk consumption and BMD in South Korean adults (≥20 years).

Methods

We analyzed men and women aged ≥20 years who participated in the Korean National Health and Nutrition Examination Survey, 2008–2011. We used linear regression to calculate the mean BMD and 95% confidence interval (CI) based on the frequency of milk consumption. Multivariate logistic regression analysis was used to estimate the odds ratios (ORs) and 95% CI for T-scores ≤-2.5 (osteoporosis) in both men aged ≥50 years and postmenopausal women.

Results

In total 8,539 subjects were studied. Drinking milk more than once a day was associated with higher BMD in the total femur and femoral neck in men aged <50 years and lumbar spine in men aged ≥50 years, compared to less than once a week. It was also associated with lower ORs for osteoporosis of the femoral neck and lumbar spine in men aged ≥50 years (OR, 0.35; 95% CI, 0.125–0.979 and OR, 0.34; 95% CI, 0.143–0.804, respectively). In postmenopausal women who consumed milk 2–6 times weekly, higher BMD and lower OR for osteoporosis were observed in the total femur (OR, 0.23; 95% CI, 0.055–0.958).

Conclusion

This study suggests that frequent milk consumption could potentially reduce osteoporosis incidence in South Korean adults. Further prospective study is necessary to elucidate the effect of milk consumption on BMD.

Dairy Consumption and Metabolic Health

Milk and dairy foods are naturally rich sources of a wide range of nutrients, and when consumed according to recommended intakes, contribute essential nutrients across all stages of the life cycle. Seminal studies recommendations with respect to intake of saturated fat have been consistent and clear: limit total fat intake to 30% or less of total dietary energy, with a specific recommendation for intake of saturated fat to less than 10% of total dietary energy. However, recent work has re-opened the debate on intake of saturated fat in particular, with suggestions that recommended intakes be considered not at a total fat intake within the diet, but at a food-specific level. A large body of evidence exists examining the impact of dairy consumption on markers of metabolic health, both at a total-dairy-intake level and also at a food-item level, with mixed findings to date. However the evidence suggests that the impact of saturated fat intake on health differs both across food groups and even between foods within the same food group such as dairy. The range of nutrients and bioactive components in milk and dairy foods are found in different levels and are housed within very different food structures. The interaction of the overall food structure and the nutrients describes the concept of the ‘food matrix effect’ which has been well-documented for dairy foods. Studies show that nutrients from different dairy food sources can have different effects on health and for this reason, they should be considered individually rather than grouped as a single food category in epidemiological research. This narrative review examines the current evidence, mainly from randomised controlled trials and meta-analyses, with respect to dairy, milk, yoghurt and cheese on aspects of metabolic health, and summarises some of the potential mechanisms for these findings.

The effect of milk consumption on bone and fracture incidence, an update

Milk is a major source of high bioavailable calcium in most developed countries with an average calcium content of 1150 mg/L, providing a ready means of meeting the daily requirements. Its content in other minerals, phosphorus, vitamins, iodine, proteins, potassium and various nutrients is supposed to be beneficial for skeleton growth and bone strength. Studies on the effects of milk or whey extracts in animal trials and on surrogate markers in humanlike bone remodeling markers or bone mineral density and many observational studies in large cohorts show positive effects on bone health or risk of hip fracture. Nevertheless, a few contradictory epidemiological studies showed an increased risk of hip fractures in subjects drinking higher quantities of milk. These conflicting results may be due to the large number of confounders and methodological issues as recall bias. Most of the experts state that there are no proven effect of milk consumption on the risk of hip fractures in a way or the other. Of a scientific point of view, there is no reason to remove from the diet of large populations an aliment rich in calcium and other interesting nutrients.

Dairy products and bone health: how strong is the scientific evidence?

The relevance of dairy produce for the diminishment of osteoporotic risk is still a matter of scientific debate due to the outcome of a few single observational studies. This review will address the most robust point estimate on the role of dairy products, as reported in systematic reviews and meta-analyses on randomised controlled trials in the case of bone mineralisation or prospective studies in the case of fracture risk. Plain dairy products or those fortified with Ca and/or vitamin D improve total body bone mineral content (BMC) by 45-50 g over 1 year when the daily baseline Ca intake is lower than 750 mg in Caucasians and Chinese girls. In Caucasian and Chinese women, Ca from (fortified) dairy products increases bone mineral density (BMD) by 0·7-1·8 % over 2 years dependent on the site of measurement. Despite the results on BMC, there are currently no studies that have investigated the potential of dairy products to reduce fracture risk in children. In adult Caucasian women, daily intake of 200-250 ml of milk is associated with a reduction in fracture risk of 5 % or higher. In conclusion, the role of dairy products for BMC or BMD has been sufficiently established in Chinese and Caucasian girls and women. In Caucasian women, drinking milk also reduces fracture risk. More research on the role of dairy products within the context of bone health-promoting diets is needed in specific ethnicities, other than Chinese and Caucasians, and in men.