It has been ingrained in us time and time again that dairy builds strong bones, but could it actually be harmful for our bones? Or perhaps it’s not harmful, but it doesn’t actually help preserve bone density.
In an Endocrinology course I once took my professor, Tyrone Hayes an Endocrinology research scientist, remarked one day that the regions in the world with the highest levels of dairy consumption also had the highest rates of osteoporosis. The statement intrigued me and I continued to wonder about it.
It’s been studied but not explicitly proven that dairy is acidifying for the body and because of this calcium is leached from bones to act as a neutralizer. However, my professor didn’t mention anything about the inflammatory nature of dairy as the culprit in osteoporosis.
He hypothesized that the heavy intake of dairy in regions of the world like the US and Northern Europe was leading to the ingestion of too much calcium, throwing off the balance of hormones responsible for orchestrating bone mineralization. And, that this was especially detrimental for women at the vulnerable time of menopause, when the bone protective hormone estrogen is in rapid decline.
What he said made sense to me, but I also wondered if there could be something more going on. From an evolutionary standpoint we’re not meant to drink milk after weaning. In fact we stop making enzymes to break down lactose by the age of five or so. Yet we have continued to source milk from cows, mainly. This is one reason that I remain skeptical about the healthfulness of dairy.
Few people actually continue to breakdown lactose, while most of us display signs of lactose intolerance and inflammation whether we recognize them—or choose to ignore them—or not. However, the evidence is inconclusive on whether dairy itself has a direct negative impact on bone.
It is vitamin D that we need to be getting more of, especially the older we get. Milk doesn’t contain any vitamin D naturally, and it doesn’t contain enough even if it’s fortified with it.
We don’t need as much calcium as indicated per current dietary guidelines, plus it’s available in many non-dairy food sources like leafy greens, nuts, canned fish, and certain fruits. No one has to eat dairy to get calcium in adequate amounts.
In the US a daily calcium intake of around 1,000 mg is recommended. In countries with lower rates of bone fractures like Japan, the intake of calcium is about a third of that.
In a large observational study published in the American Journal of Clinical Nutrition, over 70,000 postmenopausal women were analyzed for a period of eighteen years. The researchers pointed out that “milk is a primary source of calcium and vitamin D, and therefore might be expected to decrease osteoporotic bone loss, however research has not generally supported this assumption.”
They found that adequate vitamin D intake—not calcium—is associated with a lower risk of osteoporotic hip fractures in postmenopausal women and emphasized that the best natural source of vitamin D is sunlight.
In his 2006 article “Ask the Expert: Vitamin D and Chronic Disease Prevention,” Edward Giovannucci, MD, Professor of Nutrition and Epidemiology at Harvard University, explained that “milk alone is unlikely to be an adequate source of vitamin D…Each glass of fortified milk should contain about 100 IU of vitamin D but on average, it may contain only 50 IU.”
“Several randomized trials found that individuals who received 800 IU per day of vitamin D lowered their risk of osteoporosis; trials that provided only 400 IU per day did not show this benefit. So someone would have to drink at least 8 glasses of milk per day to get 800 IU of vitamin D. Moreover, most experts now conclude that 1,000 to 2,000 IU per day of vitamin D may be what we need for optimum health.”
In colder climates during the winter months there might not be enough sun to provide for sufficient vitamin D production in the skin but supplements can do the job of increasing vitamin D levels. Other than that fatty fish is, according to Giovannucci, “the only good natural source of vitamin D. A 3.5 oz serving of cooked salmon, for example, has 360 IU of vitamin D; 3 oz of canned tuna has 200 IU; and 1 3/4 oz of canned sardines has 250 IU.”
Ladies, if you are premenopausal the time to work on building your bone density is now.
Bones are not merely idle structures within our bodies; they are living, ever-changing organs, responding to stresses like changes in weight bearing at every second of the day. Bone cells called osteoclasts spend their time clearing old bone so that cells called osteoblasts can come in and lay down new bone.
Estrogen keeps the osteoclasts in check so that they don’t mow down too much bone before osteoblasts can deposit new bone.
Before women reach their thirties bone building exceeds bone demolition. After that it starts to level out. Once women reach menopause estrogen levels plummet and osteoclasts are not well controlled; bones start to become porous and fragile.
In men, testosterone enters bone tissue where it is locally converted to estrogen. Men don’t experience bone loss as severely as women do because, while they do experience a decline in testosterone, it doesn’t start to dip until later in life and tapers off more evenly.
For both sexes, exercise is one of the most effective ways to increase bone density.
The heavy consumption of calcium through dairy products combined with the lack of adequate sunlight and concomitant deficiency in vitamin D production is probably the biggest reason behind the link between the incidence of osteoporosis and dairy consumption in countries that get limited light and/or long periods of cold weather.
The take home message is: Don’t think of milk as a preventative measure against osteoporosis, especially once menopause hits. And, if you don’t like milk or it doesn’t agree with you then you’re not missing anything, you can get calcium from other sources.
I think the best strategy to improve and preserve bone density is to enjoy dairy in moderation (I mean, good luck keeping me away from cheese samples at the market, especially if they’re vintage cheddar) get some sun, exercise, and supplement if necessary with vitamin D.