Friday Favorites: Bone Density, Fracture Rates, and Vitamin D in Vegans

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Intro: This video and the next explore whether there is a difference in bone density between those who eat meat and those who don’t.

Osteoporosis has become a major public health problem worldwide. The morbidity and even mortality of osteoporotic complications, such as hip fractures, are severe. Osteoporosis is diagnosed by testing low in bone mineral density and afflicts about 1 in 20 men over age 65, and 1 in 4 women. Do we need to be concerned about bone mineral density in vegetarians and vegans?

There are studies showing vegetarian-style diets during adolescence can have a positive impact on bone in young adulthood, but what we really want to know is about osteoporosis at older ages. In an earlier video Do Vegans Have Lower Bone Mineral Density? I talked about a meta-analysis that concluded that vegetarian diets, particularly vegan diets, were associated with lower bone mineral density, but only by a clinically insignificant amount. Given the relationship between fracture risk and bone mineral density, the relative risk of fracture in vegans would only be about 10 percent higher than in meat-eaters. But that doesn’t sound very insignificant to me. Now, I talked about how the differences in bone mineral density are largely just a function of vegetarians, and particularly vegans, having such low rates of obesity. (Obese individuals are protected from osteoporosis because they do so much weight-bearing exercise just walking from one room to the next, basically.) But we only care about bone mineral density because we care about bone fractures.

What’s the comparative fracture risk in vegetarians vs. nonvegetarians? Now we’re talkin’. Compared with meat eaters, the same risk for vegetarians, but a 30 percent higher risk for vegans. Now, it was mostly wrist and arm fractures; there weren’t any hip fractures. Wrist fractures are among the most common fractures, and interestingly, occur typically in women who are in good health and active. It’s the kind of fracture you get if you like trip when you run, and fall on an outstretched hand. But the 30 percent increased risk was after controlling for non-dietary factors, including activity such as exercise or an active workplace. The increased risk only disappeared when they controlled for calcium. Vegans only were at higher risk when they got under 525 mg of calcium a day, which is equal to the estimated average requirement.

Among those getting at least 525 mg, there was no greater risk. So, the higher fracture risk in the vegans appeared to be a consequence of inadequate calcium intake, which is essential for bone health regardless of what kind of diet you eat. You don’t need to drink milk. A greater intake of milk and dairy products is not associated with a lower risk of osteoporosis or hip fracture. In fact, every additional cup or so of cow’s milk a day was associated with a 9 percent greater risk of hip fracture in prospective studies. But you do have to get calcium from somewhere. Plant-based sources include almonds, sesame seeds, tofu, calcium-fortified plant milks, or the best sources are dark green leafy vegetables such as kale—basically any dark green leafies except for spinach, beet greens, or chard, which are stingy with their calcium.

And most vegans in the study were getting more than the 525 mg. There are a lot of healthy foods packed with calcium, but they only work if you actually eat them. But wait; what about the mountain of data showing that dietary calcium intake is not associated with risk of fracture, and there is no evidence that increasing calcium intake prevents fractures, and so increasing calcium intake should not be recommended for fracture prevention. But that’s based on giving extra calcium to people who are already getting enough calcium. So, it may be like a plateau effect.

Take women getting only 500 mg of calcium a day, and randomize them to take calcium supplements, and you can drop hip fracture rates 40 percent within 18 months. Now, they also gave them vitamin D, and the women did start out seriously deficient, with vitamin D levels down around 15 ng/ml; so, it’s hard to tease out the effects of the calcium versus the vitamin D. But vegans who aren’t supplementing with vitamin D at higher latitudes can dip down that low during the winter months too. Now, there was a study in Shanghai that found comparable bone health despite lower vitamin D levels down around 15 ng/ml. They were also low in calcium intake, and still had similar bone mineral density. But given that fracture study, I’d recommend people make sure they’re getting enough calcium and enough vitamin D. But that fracture study was published in 2007. A 2020 update found a higher risk of fractures even in vegans getting more than 700 mg of calcium a day. What explains that? We’ll explore just that question next.

As I noted in my video on bone mineral density Do Vegans Have Lower Bone Mineral Density? vegetarians had slightly lower bone mineral density in their spines. Although the difference was basically within the margin of error for the test, if the bone quality really is compromised, it could lead to collapsed vertebrae and increased spinal fracture risk, but there is no evidence for this. The incidence of vertebral fracture was ascertained in older women who had been vegan for most of their lives—34 years on average. And despite their calcium intake being terrible, about half that of the non-vegans, and a quarter of them vitamin D deficient, the incidence of vertebral fractures was not significantly different. Although the vegans had a higher prevalence of vitamin D deficiency, and lower dietary calcium intakes, the two factors were not associated with bone loss. In fact, the annual loss in bone mineral density in the hips of vegans was less than half that of the meat-eaters, though the difference did not reach statistical significance.

Vegetarian women had not been found to be at higher risk of any kind of fractures, including wrist fractures, in this case, though among vegetarians, those who consumed the least vegetable protein intake were at the highest risk for fracture. Those who ate beans every day, or nuts, or something like veggie burgers, only had a third of the wrist fractures compared to vegetarians who only ate beans or other higher protein foods less than three times a week. So, those who consume a vegan or vegetarian diet may be at increased risk of fracture unless care is taken to ensure that an adequate quantity and variety of foods high in protein (such as whole grains, nuts, and legumes such as beans, split peas, chickpeas, or lentils) are in the diet. That’s one of the reasons in my free Daily Dozen app, I recommend whole grains and legumes every day.

Hip fractures are even more serious. Those eating legumes like beans every day reduced their risk of hip fracture by more than 60 percent, compared to 40 percent lower risk from meat protein, with plant-based meats coming in in between, with about 50 percent lower risk of hip fracture.

What’s the bottom-line on plant-based diets and bone health, according to this 2020 review? Theoretically, a long-term plant-based diet may reduce the risk of osteoporosis, but that has yet to be demonstrated. What we do know is that plant-based diets, when ensuring adequate calcium and vitamin D levels, don’t appear to have any detrimental effects on bone health. But this was published in August 2020. In November 2020, the 12-year follow-up to the study I talked about in my last video, on comparative fracture risk in vegetarians vs. non-vegetarians, was published, finding that non-meat eaters, especially vegans, had higher risks of total bone fractures, including at sites associated with osteoporosis such as hip fractures. It comes out to be about 20 more cases in vegans for every 1000 people over 10 years. So, if indeed this is cause-and-effect, eating vegan there would be an annual 1 in 500 chance of having a bone fracture that you otherwise might not have had.

Was it because they weren’t eating enough beans? Apparently not, since vegans getting more protein still apparently had higher risk. Maybe it was because they weren’t getting enough calcium? Apparently not, since vegans getting more calcium still apparently had higher risk.

What about bone and vitamin B12? If you remember, EPIC-Oxford, where the bone data come from, is the same group of British vegans who have rampant B12 deficiency. More than half the vegans were B12-deficient because they weren’t adequately supplementing with B12 or B12-fortified foods. This can lead to high homocysteine levels, which not only increase stroke risk, but may increase the activity of bone-eating cells. This was in a petri dish, but you do indeed see low bone mineral density in those born with a birth defect that leads to high homocysteine levels in the blood. Therefore, high serum homocysteine may be regarded as a factor that can reduce both bone mass and quality. But you don’t know, until you put it to the test. And homocysteine-lowering treatment failed to reduce the risk of bone fracture. So, in the end, the effect of B12 deficiency in bone health remains to be established.

Okay, so, how do we explain the higher fracture rates found among vegans? The investigators conclude that their findings suggest that bone health in vegans requires further research, but there were some clues. The elevated fracture risk, both for total fractures and for hip fractures specifically, was only significant for those under a BMI of 22.5, which is like under about 130 pounds for a woman of average height. So, part of the problem is that vegans tend to be so slender on average. Why are overweight and obese individuals protected from fractures? Think about it. They have a cushioning during a fall. There’s more of a cushion on your hips. Also, there’s an enzyme in fatty tissue that churns out estrogen, which is why women increase their breast cancer risk a percentage point for every pound they gain in adulthood. But estrogen can also have a bone-preserving effect. You can get the best of both worlds consuming soy foods, preventing bone loss while at the same time associated with lessening breast cancer risk for both estrogen receptor positive tumors and estrogen receptor negative tumors. Finally, overweight and obese individuals also may have stronger bones just from the increased weight-bearing. Carrying 100 extra pounds, you’re doing major weight bearing exercise just walking across the room! So, the risk differences they saw between vegans and meat eaters were likely at least partially due to differences in BMI.

My money, however, is on vitamin D. Great Britain is at Canadian latitudes. The sun’s rays are at such an angle during the winter months up there that the vitamin D levels among British vegans in the wintertime drop down to suboptimal levels. Ideally, we should be up around 75 nanomoles per liter or 30 nanograms per milliliter, depending on what units you’re using, which the vegans nail in the summer. It is the sunshine vitamin, after all. But in the winter, not getting the vitamin D added to dairy or found naturally in oily fish, if vegans aren’t supplementing, at that latitude during the winter, their vitamin D levels may drop too low.

Now, randomized controlled trials show that vitamin D alone doesn’t seem to reduce fracture rates, but boosting people’s vitamin D and calcium at the same time does. So, maybe it was a combination of the relatively low vitamin D and calcium intakes among the vegans that led to their higher fracture rates. We won’t know for sure until it’s actually put to the test, and when it is, you can be sure I’ll do a video.

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