字幕表 動画を再生する 英語字幕をプリント "Do Vegans Have Lower Bone Density and More Fractures?" This video and the next explore whether there's a difference in bone density between those who eat meat and those who don't. "Do Vegans Have Lower Bone Density and More Fractures?" 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 four 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, 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% 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 versus nonvegetarians? Now we're talking. Compared with meat eaters, same risk for vegetarians, but a 30% 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 occurs 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% 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 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% 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: dark green leafy vegetables such as kale --- basically any dark green leafies, except for spinach, beet greens, or chard, which are just stingy with their calcium. And most vegans in the study were getting more than the 525. There's lots 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 fractures, and there's 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 might just be like a plateau effect. Take women getting only 500 mg of calcium a day and randomize them to calcium supplements, and you can drop hip fracture rates 40% 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, so it's hard to tease out the effects of calcium versus the D. But vegans who aren't supplementing with 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 D levels down around 15. 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.