Vegan for Life - Jack Norris [18]
Today’s commercial plant foods and meats are different from the foods available in prehistoric times. We eat hybrids of plants and we feed foods to animals that they would not normally eat. Additionally, the U.S. food supply is routinely fortified with a host of vitamins and minerals. Even those people who strive to eat a more “natural” diet as adults have normally benefited from fortified foods as children. It is quite unlikely that anyone is eating a natural diet in today’s world.
Taking a daily vitamin B12 supplement is a small thing that can make all the difference in your health as a vegan. Based on our current knowledge of vitamin B12 requirements and sources, supplementation is not a subject for debate. Vitamin B12 supplements or fortified foods are an essential part of a well-balanced and responsible vegan diet at all stages of the life cycle.
CHAPTER 4
CALCIUM, VITAMIN D, AND BONE HEALTH
CALCIUM
For most of human history, people got their calcium from plants, primarily wild, leafy greens. Dairy foods didn’t become part of the human diet until around 10,000 years ago and even then they were consumed only in some parts of the world. Calcium-rich greens were so abundant in early diets that some nutritional anthropologists speculate that people consumed as much as 3,000 milligrams per day of calcium from these foods, or about three times our current recommended intakes. 1 The cultivated greens that are available to vegans today are lower in calcium than the wild vegetables available to our ancestors, but they can still make a significant contribution to calcium intake. Vegans can also get calcium from some legumes and nuts, and from fortified foods.
There is no question about whether vegan diets can provide enough calcium. They can. But that doesn’t mean that they do. In studies of vegans, average calcium intakes often fall well below recommendations. 2 One unanswered question has to do with calcium needs of people who eat plant-based diets. Do vegans need less calcium? You’ll see that it’s not so easy to figure this out.
Calcium and Bones
While bones might seem solid and static, they are actually quite dynamic. The skeleton acts as calcium storage, providing a steady supply of calcium to the blood where it is needed for muscle relaxation, nerve cell transmission, and a host of other functions. Some of this calcium is regularly lost in the urine and must be replaced by dietary sources. As a result, bones are in motion—breaking down to release calcium to the blood and then taking up new calcium and rebuilding. Getting enough calcium is important for bone health, but reducing the amount that is lost through the urine could be important too.
Bones grow through the first three decades of life, becoming longer, heavier, and denser. By their late twenties or early thirties, most people have achieved peak bone mass, and their skeleton is as heavy and dense as it is going to get. There is some evidence that peak bone mass determines bone health and risk for osteoporosis in later years.
Beginning at age forty-five or so, there is a shift in metabolism and bone mass begins to decline. Efforts to slow calcium losses from the body and provide enough calcium to keep bones strong are important for preventing osteoporosis, especially for women, who can begin to lose bone rapidly after menopause.
Good bone health depends on a complex interplay of factors that affect both absorption of calcium and calcium losses from the body. Diet, lifestyle, and genetics all play a part in calcium balance. Figuring out how these factors interact and affect calcium needs has been an ongoing subject of debate among researchers, and some of the issues may be especially important for vegans.
The Relationship of Calcium Intake to Bone Health
Calcium is different from other nutrients in that it isn’t associated with an acute deficiency disease.