By Jack Norris, RD
Americans are regularly being urged to consume more calcium in order to prevent osteoporosis. It is practically impossible to meet the recommendations without large amounts of cows’ milk, calcium-fortified foods, or supplements.
Because vegans do not eat dairy products, without fortified foods or supplements their calcium intakes tend to be low (about 400-600 mg per day compared to the U.S. recommended intake of 1,000 mg per day).
Traditionally, the vegan community has responded to this by saying osteoporosis is a disease of calcium loss from the bones, not a lack of calcium in the diet. This was based on two ideas.
The first idea is that ecological studies have shown that the countries with the highest intake of dairy products (northern Europe and the USA) have higher rates of hip fractures than do Asian and African countries where much less milk is consumed. This in turn, can be explained by the second idea, which is that studies show that after ingesting animal protein, people urinate large amounts of calcium.
Therefore, the thinking goes, calcium intake isn’t important for preventing osteoporosis and vegans are protected due to the lack of animal protein in their diets.
Unfortunately, there is a lot of evidence to suggest that this is not correct. It turns out that hip fractures are more indicative of the risk of falling than of osteoporosis in some countries, with a recent study from Hong Kong showing that while men and women in Hong Kong had lower rates of hip fractures, they had higher rates of vertebral factures, and the women had higher rates of osteoporosis than Caucasian women.
As for protein leaching calcium from bones into the urine – it’s a lot more complicated than that. The studies that showed calcium to be urinated out were done using protein isolates whereas eating protein from whole foods does not result in a calcium imbalance. Population studies and clinical trials show that protein, including animal protein, does not have a negative effect on bones (more details here).
So where does that leave vegans?
Vegans’ bone mineral density, a measure of osteoporosis, has been shown in many studies to be slightly lower than non-vegans. More importantly, the one study on Western vegans measuring fracture rates over time found that vegans in the group who got less than 525 mg of calcium per day had a higher fracture rate than vegans in the group getting more than 525 mg. The vegans in the lower calcium group also had higher fracture rates than the meat-eaters and lacto-ovo vegetarians.
Although it is possible to meet the calcium recommendations by eating greens alone, the average vegan probably will not meet recommendations without drinking a glass of fortified drink each day, eating calcium-set tofu, or taking a 250 – 300 mg supplement (in addition to eating an otherwise balanced diet).
The greens highest in absorbable calcium are kale, mustard greens, bok choy, turnip greens, collards, and watercress. In addition to calcium, greens also contain vitamin K, potassium, and magnesium, which also contribute to better bone health.
While spinach, Swiss chard, and beet greens are high in calcium, it is not well absorbed due to their also high content of oxalates, which bind calcium and prevent absorption from the digestive tract.
Research is mixed about whether calcium intakes above 1,400 mg per day can put people at risk for chronic disease. If you take a calcium supplement, it’s best not to go overboard. Most vegans taking 250-300 mg per day would not come close to 1,400 mg.
Vitamin D is also important for bones, as it can increase calcium absorption when the body signals that it needs calcium. Research has shown that in populations with calcium intakes similar to omnivores in the United States, vitamin D is more important than calcium for preventing osteoporosis.
In recent years, vitamin D has also been linked to many other diseases and some researchers have suggested that the recommended vitamin D levels are too low. However, the Institute of Medicine has reviewed the research and concluded that is not the case. The controversy has resulted in many people thinking they are deficient in vitamin D when they are not.
The only significant, natural, dietary sources of vitamin D are fatty fish, eggs (if chickens have been fed vitamin D), and mushrooms (if treated with UV rays). Most Americans get their dietary vitamin D through fortified milk and fortified margarine. The vegan diet contains little, if any, vitamin D without fortified foods or supplements. On average, vegans’ vitamin D levels are adequate, but somewhat lower than non-vegans.
Most people get a significant amount of their vitamin D from the action of UV rays on their skin. While the body can store vitamin D made in the sunnier months for use during less sunny times, this does not work for everyone. In fact, some people, even those living in sunny climates, develop extremely low levels of vitamin D. This can manifest itself through fatigue and bone pain.
If your arms and face (or the equivalent amount of skin or more) is exposed to the following amounts of midday sun (10 am to 2 pm), without sunscreen, on a day when sunburn is possible (i.e., not winter or cloudy), then you should not need any dietary vitamin D that day:
• Light-skinned: 10 to 15 minutes
• Dark-skinned: 20 minutes
• Elderly: 30 minutes
On all other days, people older than one year should get 600 to 1,000 IU of vitamin D.
Due to skin cancer concerns, some dermatologists recommend getting all your vitamin D from supplements rather than the sun. The amounts of sun above for light and dark-skinned people should be safe, but I have not seen research on how much sun is safe for elderly people and recommend talking to your doctor about how to get vitamin D if you believe you are at risk for skin cancer.
600 to 1,000 IU of vitamin D is only available in supplemental form or specially treated mushrooms.
There are two forms of supplemental vitamin D: D2 and D3. Vitamin D2 is always vegan, made from exposing fungi to UV rays. Vitamin D3 normally comes from fish oil or sheep’s wool, but there is a vegan version made by Vitashine.
A great deal of research has been conducted on vitamin D2 and D3. Vitamin D2 is effective at increasing bone mineral density (when given to people who are deficient). Vitamin D2 can also increase vitamin D levels temporarily, but is not as effective as vitamin D3 at keeping vitamin D levels raised when taken only weekly. If you take vitamin D on a regular basis, D2 should be fine, whereas if you are only going to take it sporadically, without getting sun in the interim, or find that your vitamin D levels will not increase on D2, then you should opt for D3.
If you are trying to raise your vitamin D levels with D2, make sure the laboratory can detect vitamin D2, and not just vitamin D3. Also make sure that you are not trying to raise your levels beyond what the Institute of Medicine recommends of between 40 and 50 nmol/l (16 and 20 ng/ml) as there’s no sense in worrying if you cannot seem to get your vitamin D levels twice as high as what is recommended!
This article was written by Jack Norris, a Registered Dietitian and President and co-founder of Vegan Outreach. Vegan Outreach produces Why Vegan and other booklets and their Adopt a College program hands booklets to over 750,000 students every semester. In 2005, Jack was elected to the Animal Rights Hall of Fame.
Along with Ginny Messina, MS RD, Jack has written the book Vegan For Life: Everything You Need to Know to Be Healthy and Fit on a Plant-Based Diet.