Vegan for Life (8 page)

Getting calcium from plants might seem a little strange in a society that is so focused on dairy foods as a source of calcium. But some research suggests that even omnivores get as much as 40 percent of their calcium from plant foods. And really, why should that be surprising? Omnivores eat broccoli, baked beans, hummus, and other plant foods that are good sources of calcium.

While a strong dairy lobby has convinced many consumers that milk and other dairy foods are essential for a healthy diet, the ability to
drink milk into adulthood is not the norm throughout the world. Normal development throughout most of the world involves a gradual loss of the enzyme needed to digest milk sugar after children are weaned from breast milk. Indications are that a mutation occurred some ten centuries ago among northern Europeans that resulted in the continued production of this enzyme, allowing that population to drink milk into adulthood.

In the United States, we refer to the lack of this enzyme as “lactose intolerance.” But that’s definitely a western bias since this “intolerance” is not a lack or an abnormality; it’s part of normal human development in most people. Since many people the world over need to meet calcium needs without dairy foods, there is no reason why vegans can’t do it as well. And with our access to a wide variety of calcium-rich and fortified foods, it’s not at all difficult.

The amount of any nutrient in a food is not equal to the amount that actually makes its way from the intestines into the bloodstream. The bioavailability of a nutrient from a particular food refers to the amount of that nutrient that is likely to be absorbed and used, and it’s affected by a number of factors.

A few leafy green vegetables—spinach, beet greens, Swiss chard, and rhubarb—are high in naturally occurring compounds called oxalates that bind calcium and make it essentially unavailable to the body. But the availability of calcium from low-oxalate vegetables—kale, collards, broccoli, and turnip greens—can be as high as 50 percent.
¹⁶
Calcium absorption from soyfoods, like calcium-set tofu (tofu that is processed with calcium-sulfate) and fortified soymilk, is around 25 to 30 percent, which is about the same as from cow’s milk. Calcium absorption from nuts and legumes is somewhat lower, around 20 percent.

The recommended intake of 1,000 milligrams of calcium is based on the assumption that most people absorb around 30 percent of the
calcium in their diet. If you’re eating a varied diet that includes several different types of calcium sources, including leafy greens and soy products, you don’t need to worry that some of the calcium from other foods is absorbed less efficiently.

It’s possible to get plenty of calcium just from eating foods that are naturally rich in this mineral, but it does take some effort. (This is equally true for people who consume dairy foods, since many people who drink milk don’t meet calcium requirements. That’s why so many products on the market—from cereals to juices to protein bars—are fortified with calcium.) Using fortified foods like juices and nondairy milks can make it easier to meet calcium recommendations on a vegan diet.

It’s also helpful to pay attention to the effects of processing. For example, frozen leafy greens are higher in calcium than fresh, although this is simply because their volume tends to be more concentrated. Processing also affects the amount of calcium in different types of tofu. Tofu production involves ingredients that cause soymilk to curdle. The two most common—often used together—are magnesium-chloride (
nigari
in Japanese) and calcium-sulfate. When calcium-sulfate is used, tofu is often an excellent source of calcium. Also, firm tofu tends to have a higher calcium content than soft. It’s important to read package labels, though, since the amount of calcium in different brands and different types of tofu varies widely.

In the Vegan Food Guide in Chapter 7, we recommend 6 to 8 servings of calcium-rich foods per day. This allows you to mix and match small servings of a variety of calcium-rich foods or get all of your calcium from larger amounts of just a few foods. One serving is ½ cup fortified plant milk or juice, ½ cup cooked, calcium-rich vegetables, ½ cup tofu or tempeh, 2 tablespoons almond butter or tahini, ¼ cup soynuts, or ½ cup dried figs. The table on page 45 shows calcium contents of a wide variety of plant foods.

Adequate vitamin D is every bit as important as calcium for maintaining bone health. But is vitamin D a nutrient? Not exactly, since we can make all we need when our skin is exposed to ultraviolet rays from sunlight. In fact, for most of human history, this is where people got their vitamin D since it occurs naturally in very few foods. But as people moved away from the equatorial zones and began to spend more time indoors, vitamin D deficiency became a problem. In the early 1900s, rickets (soft bones that don’t develop well in children) was a significant public health problem that led to fortification of cow’s milk with vitamin D.

While the focus has long been on bone health, more recent research suggests that suboptimal vitamin D levels are linked to fibromyalgia, rheumatoid arthritis, multiple sclerosis, depression, muscle weakness, diabetes, hypertension, and cancer. The current AI for vitamin D in adults is 600 IUs (vitamin D is also measured in micrograms; 1 microgram equals 40 IUs). But many experts believe that it may take as much as 1,000 IUs or 25 micrograms to maintain ideal blood levels of vitamin D.
¹⁷
While this continues to be a controversial area, we favor the higher recommendation.

The only significant, natural sources of vitamin D in foods are fatty fish, eggs from chickens who have been fed vitamin D, and mushrooms treated with ultraviolet rays. Many people think that milk is a good natural source of vitamin D, but it isn’t. Milk contains no vitamin D unless it has been fortified and is no more natural a source of this vitamin than any other fortified food.

There are two types of vitamin D used in fortified foods and supplements. Vitamin D
₃
or
cholecalciferol
is derived from animals, usually from sheep’s wool or fish oil. Vitamin D
₂
or
ergocalciferol
is usually obtained from yeast and is vegan. The evidence suggests that the two types are absorbed equally as well but that blood levels of vitamin D
₂
decline more quickly when megadoses of the vitamin are consumed.
^18
,
19
At the smaller dose that we recommend—1,000 milligrams per day—vitamin D
₂
appears to be as effective as vitamin D
₃
.

Concern about skin cancer has people using powerful sunscreen or shying away from sun exposure altogether. However, in addition to blocking the harmful effects of the UV light on the skin, sunscreen blocks vitamin D synthesis. And there are plenty of other factors that affect vitamin D synthesis in the skin. Older people need longer exposure and so do people with dark skin. Smog can interfere with vitamin D synthesis and the farther away you are from the equator, the more sun exposure you need to make vitamin D. Some research suggests that Americans living in the northern part of the country do not make any vitamin D during the winter months.
²⁰

To make adequate vitamin D for one day, a light-skinned person needs ten to fifteen minutes of midday (10:00 a.m. to 2:00 p.m.) sun exposure, without sunscreen, on a day when sunburn is possible.
²¹
Dark-skinned people need twenty minutes and older people need thirty minutes.
^22
,
23

If your sun exposure doesn’t match these guidelines, then you need to take a supplement or use fortified foods. We recommend 25 micrograms (1,000 IU) per day of vitamin D
₂
.

Many foods, including most breakfast cereals, are fortified with vitamin D. Almost all use vitamin D
₃
, which is derived from animals. Most brands of fortified soymilk and other nondairy milks use vitamin D
₂
, which comes from yeast exposed to UV rays.

For food labeling purposes, the Daily Value for vitamin D is 10 micrograms (400 IU). So if a food provides 25 percent of the Daily Value for vitamin D, it contains 2.5 micrograms (100 IU) of vitamin D per serving. Vitamin D–fortified soy, almond, hemp, or rice milk normally has 2 to 3 micrograms (80 to 120 IU) per cup. You can see from these numbers that it’s not that easy to meet the recommended 1,000 IU per day from fortified foods. If your sun exposure isn’t adequate, you will probably need to use a vitamin D supplement. Most natural foods stores carry supplements of plant-derived vitamin D
₂
, or you can order one from the online sources in the resource section of this book.

Calcium and vitamin D have well-deserved reputations as bone-strengthening nutrients, but they don’t act alone. The following are all important for protecting bone health.