Elsevier

Joint Bone Spine

Volume 84, Issue 3, May 2017, Pages 275-281
Joint Bone Spine

Review
Osteoporosis: Is milk a kindness or a curse?

https://doi.org/10.1016/j.jbspin.2016.06.006Get rights and content

Abstract

Cow's milk is often severely criticized as a cause of multiple health problems, including an increased risk of fractures. A close look at the scientific literature shows a striking contradiction. On the one hand, experimental studies of surrogate markers (e.g., bone turnover markers and bone mineral density [BMD]) usually indicate benefits from drinking cow's milk. On the other, the findings from epidemiological studies are conflicting and disconcerting. In all age groups, including children and postmenopausal women, consuming cow's milk, powdered milk supplements, or whey protein is associated with a slower bone turnover and unchanged or higher BMD values. These benefits are particularly marked in populations where calcium deficiency is prevalent, for instance in Asian countries. No interventional studies have addressed the fracture risk potentially associated with drinking cow's milk. The only available data come from epidemiological observational studies, whose results are conflicting, with a lower fracture risk in some cases and no difference or a higher risk in others. Several hypotheses have been offered to explain these findings, such as a deleterious effect of D-galactose, lactose intolerance, and acid overload. Epidemiological studies face many obstacles when seeking to detect effects of a single food, particularly the multiplicity of interactions among foods. Furthermore, reliable dietary intake data must be collected over prolonged periods, often long before the occurrence of a fracture, and defective recall may therefore introduce a major yet often unrecognized bias, particularly in populations where calcium deficiency is uncommon. To date, there is no conclusive evidence that we should modify our currently high level of consumption of cow's milk.

Section snippets

Introduction: cow's milk in the dock

For many years, cow's milk has been vociferously accused of harming human health. This hostility is fed by a conspiracy theory suggesting that the dairy industry will go to any lengths to sell its produce and has bribed medical experts, scientific societies, and public health authorities into encouraging the consumption of milk. Milk, a complex food that has been consumed by humans in large amounts for millennia, is thus accused of causing numerous diseases that range from prostate and ovarian

Studies of bone turnover and BMD vs. studies of fractures: disturbing discrepancies

Humans have been consuming large amounts of milk for several thousands of years. The nutritional properties of milk are remarkable. Milk is an abundant source of calcium, whose bioavailability is high compared to other dietary sources, and the calcium/phosphate ratio in cow's milk is optimal for ensuring bone mineralization. The mean calcium content in whole and skim milk is 1150 mg/L, providing a ready means of meeting the daily requirement of 900–1200 mg. Milk is a well-balanced food, with

Milk consumption slows bone remodeling and protects bone mass in all age groups

In children and adolescents, who normally have a fast pace of bone turnover to meet the needs of skeletal growth, a high milk intake suppresses the secretion of parathyroid hormone (PTH) [2] and decreases the levels of bone resorption markers, while enhancing bone growth, whereas a high intake of meat does not share these effects [3]. In healthy postmenopausal women, milk supplementation also lowers the levels of bone turnover markers [4], [5], [6]. The effect of milk or any other source of

Whey: a side-product with pivotal effects?

The benefits of milk are chiefly mediated by calcium and proteins, such as casein. Other components may also have favorable effects on bone, however. Several studies, many conducted in Asia, looked at the effects of whey protein on bone. Whey is the liquid left after curdled milk is strained. In mice, whey proteins diminished bone turnover [28], increased BMD and mechanical strength of the femur [29] and possibly promoted fracture healing [30]. Whey protein intake increased lumbar spine BMD in

Milk and fractures: a jumble

Findings from epidemiological studies are not always consistent with those of surrogate endpoints such as bone turnover markers and BMD. Several obstacles exist to the demonstration of effects in epidemiological studies. One is the large number of interactions among nutrients in populations that are not always calcium-deficient. Another is the challenge raised by measuring food intakes, particularly retrospectively, which introduces multiple sources of bias. The occurrence of a fracture is a

Which mechanisms might underlie harmful effects?

Many mechanisms have been suggested to explain the possible harmful effects of milk components on bone. In subsamples of the two above-mentioned Swedish cohorts, milk intake was positively associated with urine levels of 8-iso-PGF2α, a marker for oxidative stress, and with serum levels of interleukin 6, a marker for inflammation [1]. Another study by the same group demonstrated a negative association between urinary 8-iso-PGF2α and BMD [54]. In the same study, the intake of fermented dairy

Sources of bias in available studies

One possible source of bias is the reverse causality bias, in which individuals with known risk factors for osteoporosis increase their milk intake [57]. Recall bias may act in two different directions: some individuals may have only limited recollections of their diet during childhood and adolescence and, on the other hand, individuals with a history of events such as a fracture or diagnosis of osteoporosis may be more likely to remember whether they consumed foods known to affect bone, such

Conclusion

The controversy about cow's milk and fractures is occurring within a climate of mistrust directed at science, technologies, and the industries that use them. Léon Guéguen, a former researcher at the French national agronomy institute (INRA), aptly summarized the situation: “A growing number of people claim that the human body cannot handle a high-calcium intake, because milk has been available for only a few thousand years and cow's milk is not designed for humans, which are the only animals

Disclosure of interest

Patrice Fardellone has received honoraria from Candia, Amgen, BMS, Expanscience, Lilly, and MSD.

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