Is Dairy Good For Your Bones?

A glass of milk with each meal was nonnegotiable for us as kids.  But does it really do a body good?  The idea that milk and dairy products have no effect or may even weaken bones has recently gained significant public traction.

There is of course logic in consuming dairy products for bone health.  Dairy products contain more bone-beneficial nutrients per calorie than any other food group.  It’s like adding money to a savings account… the more you add the more money you have in the long-term, right?  Getting 3-servings of low or non-fat dairy per day helps build your bone bank account.

Our team of internationally recognized nutrition researchers set out to answer just that question.  We used what scientists call a systematic review to assess the totality of human evidence on dairy intake and bone health across the lifespan.  And here’s what we found…

Dairy consumption is associated with fewer fractures in older adults and it’s also important in adolescents for building strong bones.  Overall, we found 90 human studies, including 30 randomized controlled clinical trials that assisted us in making our recommendations and highlighting several research gaps.  For instance, there is a need for studies in infants, toddlers, and young adults.

Our team utilized a common grading scale to describe the available evidence by life stage.  

• Infants and toddlers (D-grade or insufficient evidence)
• Children (D-grade or insufficient evidence)
• Adolescents (C-grade or limited evidence)
• Young adults (D-grade or insufficient evidence)
• Older adults (B-grade or moderate evidence)

It is important to note that grading scales used in systematic reviews are not exactly like those used in education.  In systematic reviews, grading scales are used to indicate how strongly a recommendation is supported by the totality of evidence.  This methodology is far from perfect and has been largely adopted from the much more straightforward field of medicine.  A grade of “insufficient evidence” denotes a lack of adequate research to support a particular recommendation.  Grading scales and ascertaining actual effects of nutrition interventions are immensely complex.  

Let’s compare calcium and aspirin. When you have a headache, you take an aspirin to alleviate the headache. There is a true placebo. You either took the aspirin or you didn’t. Unless you’re taking a bunch of other medications (not common in clinical trials of drugs) there isn’t much to inhibit that aspirin from curing the headache. Maybe bigger people need a higher dose and there are some genetic differences between folks, but for most part it's relatively straightforward and we can easily say that there is “A” level or “strong evidence” that taking an aspirin can alleviate a headache. Calcium on the other hand, requires the body to have adequate blood levels of vitamin D to absorb calcium and put it into your bones. Blood levels of vitamin D are somewhat dependent on an individual’s magnesium status (as well as several hormones) that is also somewhat interrelated to sodium, potassium, and oh yes, calcium status. That’s a very simplistic snapshot of the biochemistry.

Since the end of World War II, the international Declaration of Helsinki has forbidden unethical research on human subjects, such as depriving an individual of an essential nutrient like calcium.  Therefore, nutrition researchers often look to population data when assessing whether lower habitual intakes of nutrients like calcium have a long-term detriment to bone.  Observational evidence is subject to confounding and heavily relies on self-reported intake (i.e., how many fluid ounces of milk did you consume last week?).  Lots of room for inaccuracy.  Due to the multifactorial nature of nutrition and its perceived incremental effects on health over time, most recommendations are likely to never obtain “A” grade or “strong evidence” using methods and systems adopted from the field of medicine.

Our findings are also not surprising since bone deterioration and resulting osteoporotic fractures are more likely to occur in older adults as compared to younger subpopulations.  Contrary to popular belief, less than half of the studies were funded by the food or dairy industries and there was no difference in outcomes based on funding source.

The takeaway message.  Choose a diet that is nutrient-dense that incorporates low and non-fat dairy products. This is particularly important for adolescents, so that they reach peak bone mass and in older adults to prevent the onset of osteoporosis.  For more information on eating for health bones visit American Bone Health.

View the article "Dairy Intake and Bone Health Across the Lifespan: A Systematic Review and Expert Narrative" here.