October 14, 1999, WEST LAFAYETTE, Ind.-- An examination of the amount of calcium in strict vegetarian diets that exclude dairy products has found that these diets, known as vegan, lack the calcium needed to prevent osteoporosis later in life.
Vegan diets are not likely to provide enough calcium, the dietary review concluded, even if people avoid salt, protein, caffeine and other substances that increase calcium loss.
Connie Weaver, head of Purdue University's Department of Foods and Nutrition, says she doubts that many people could follow such a strictly limited diet. "A lot of vegetarians include milk in their diets, so getting enough calcium isn't a problem," she says. "But if they give up dairy products, and don't eat calcium-fortified foods, I don't know how they're going to do it."
Weaver, together with William R. Proulx of Appalachian State University and Robert Heaney of Creighton University, examined various foods to determine their levels of calcium, the rate of absorption of calcium from these foods, and how other components such as protein, salt or caffeine influenced the calcium requirements.
The authors concluded, "For most individuals in a Western culture, liberal consumption of dairy products is the easiest approach and is the least restrictive with regard to consumption of protein, salt or caffeine."
The research was published in the September issue of The American Journal of Clinical Nutrition and was funded by the National Institutes of Health.
Weaver said many nondairy foods contain calcium, and many vegan diets substitute vegetables for dairy products. But the amount of calcium in vegetables is very low compared to dairy products, and many of the vegetables also contain substances that block the body's ability to absorb the calcium.
"Broccoli is very well absorbed by the body and contains a good amount of calcium for a vegetable. But how much broccoli would you have to eat? We did the math for you," Weaver says.
The study found that four-and-a-half servings of broccoli offer the same amount of calcium as one cup of milk. A person forsaking dairy products would need to eat as many as 20 servings of broccoli each day to get enough of the nutrient.
"Another good example is kale. Kale is readily absorbed. But are people really going to eat 10 servings of kale a day? Get real," Weaver says. "On a practical level it's virtually impossible to get the calcium level you need without drinking milk in a Western diet or without adding fortified foods or supplements."
Some proponents of vegetarianism have said that because protein increases the urinary loss of calcium, vegetarians don't need as much calcium as the Daily Reference Intake suggests. "When I heard that I said 'Wait a minute. Some vegetarian diets are higher in protein than animal-based diets,'" Weaver says. "Dietary protein does influence calcium loss, but being vegetarian does not automatically reduce the risk of calcium deficiency."
In 1997, the National Academy of Science suggested that adults need 1,000 to 1,300 milligrams of calcium per day, depending on their age, about the same as three to four and a half cups of milk or yogurt per day.
Achieving the recommended daily amount of calcium can be complex. Not only do foods vary greatly in the amount of calcium they contain, but also the body absorbs the calcium in different foods differently. For example, the vitamin D in milk aids in calcium absorption, but spinach, which is high in calcium, also contains oxalic acid, which binds with the calcium and prevents the body from absorbing 95 percent of it. Foods with high levels of sulfur amino acids, such as cereals, nuts and seeds, also reduce retention of calcium.
This creates a problem for vegans because these foods are often the only sources of protein in their diets. Eliminating these foods to help increase the absorption of calcium would cause a serious nutritional deficiency and would greatly limit the choice of foods available for the diet.
"It would be difficult to substitute plant foods for dairy products to meet the calcium requirements. The volumes of vegetables that you need are just ridiculous," Weaver says. "We have choices. You can reduce protein and salt and try to get enough vegetables, or you can drink milk and not worry about it. Alternatively, calcium can be obtained from fortified foods and supplements."
Calcium is the most common mineral found in the body, and it is used in many body functions, such as muscle movement, including the heart. Bones contain much of the body's calcium, and as the body ages it gets some of the calcium it needs by slowly breaking down bone material. Excessive loss of bone material and minerals results in osteoporosis.
Osteoporosis causes bones to weaken, resulting in a greater risk of fractures and other injuries. In severe cases, osteoporosis also can cause a person's shoulders to round and the upper back to deform, resulting in the unfortunately familiar dowager's hump.
Osteoporosis affects 35 million Americans, four out of five of whom are women, at an annual cost of $13 billion.
Writer: Steve Tally, 765-494-9809, tally@aes.purdue.edu
Related Web site:
Connie Weaver's home page, http://www.cfs.purdue.edu/fdsnutr/people/weaver.html
Journal
American Journal of Clinical Nutrition