In addition, there are four things almost everyone can do to reduce the chances of developing osteoporosis and fractures:
• Be as physically active as possible. Engage in a variety of activities to keep your bones healthy and your muscles strong.
• Take 800 to 1,000 IU of vitamin D a day. Many multivitamin brands contain this much.
• Get enough vitamin K. You can do this by eating at least one serving of green leafy vegetables a day.
• Don’t get too much extra preformed vitamin A (retinol) unless prescribed by your doctor. Keep your daily dose from supplements under 2,000 IU.
CHAPTER ELEVEN
* * *
Take a Multivitamin for Insurance
VITAMINS WERE ONCE THOUGHT OF as nutrients needed in small amounts to prevent diseases with exotic-sounding names like beriberi, pellagra, scurvy, and rickets. Early nutritional guidelines for vitamins focused on the amount needed to avoid these diseases. As they became rarer and rarer during the twentieth century, it seemed that the vast majority of Americans were getting enough vitamins. Getting more than the amounts needed to prevent these so-called deficiency diseases, so the thinking went, was a waste. Or, as a colleague of mine once wrote, vitamin supplements may not do much other than give Americans the “richest urine in the world.”1
Some innovative thinking and the wonderful, logical conversation of science has been changing the way we think about vitamins, minerals, and other micronutrients. The biggest shift has been the realization that many chronic diseases, such as heart disease and some cancers, could be partly due to nutrient deficiencies, just like beriberi and scurvy. New findings suggest that some people—probably many people—don’t get enough of these essential micronutrients. By increasing the amount we get, mostly from food but maybe from supplements as well, we can substantially improve our long-term health.
What blew the cover off the old vitamin-deficiency-disease connection was the discovery of a direct link between inadequate intake of the B vitamin folate (also called folic acid) and birth defects such as spina bifida and anencephaly. Both of these, collectively called neural tube defects, happen when the tissues destined to become the spinal cord, the bony tube that protects it, and the brain don’t develop as they should during the first twenty-eight days of pregnancy. Spina bifida can cause paralysis and other disabilities. Children with anencephaly are born without most of the brain and spinal cord; they are either stillborn or survive for only a short time after birth. Worldwide, about 300,000 babies are born with neural tube defects each year.
Neural tube defects were most common in poor populations with poor diets. That connection prompted a search for nutritional causes. In 1976, a British team found that mothers of children with neural tube defects had relatively low levels of micronutrients.2 Other teams discovered that drugs that interfered with folic acid also increased the risk of having a child with a neural tube defect. The not-uncommon scientific seesaw followed: some studies implicated low folic acid in these birth defects, others didn’t; some small trials showed a benefit for folic acid supplements, while others didn’t. In the end, two large trials gathered conclusive proof that women who didn’t get enough folic acid were much more likely to have a child with spina bifida or anencephaly, and that taking folic acid supplements could prevent about 70 percent of these birth defects.3 This was truly a remarkable achievement for a simple and cheap vitamin pill.
At first, the recommendations on folic acid were cautious. Initial guidelines from the Centers for Disease Control (CDC) in 1991 were aimed only at women who had already had a child with a neural tube defect. A year later the CDC broadened its message, recommending that all women who could become pregnant get 400 micrograms of folic acid a day—more than double what had been recommended before. Because many women were not heeding this advice, the U.S. Food and Drug Administration took the extraordinary step of requiring that folic acid be added to most enriched breads, flours, corn meals, pastas, rice, and other grain products along with the iron and other B vitamins that have been added for years. This has boosted the average intake of folic acid by about 100 micrograms per day.
This extra folic acid helps prevent about 1,300 neural tube defects a year.4 There is now substantial evidence of unintended but extremely welcome side effects from folic acid fortification: less cardiovascular disease and cancer. As described later, low folic acid has been implicated in both of these.
This chapter doesn’t exhaustively review all vitamins and minerals. Instead it touches on those with newly recognized or suspected roles beyond the classic deficiency diseases. Along the way, it points out how to get more vitamins and minerals in your diet and which ones you might want to, or need to, get from a supplement. The table on pages 237–239 lists the current recommended daily intake of vitamins and minerals.
WHAT ARE VITAMINS?
The classic definition of vitamin is this: a carbon-containing compound essential in small quantities for normal functioning of the body. In plainer English, vitamins are a type of nutrient your body can’t make but must get from food. Vitamins are usually classified as either fat soluble or water soluble. Fat-soluble vitamins like vitamin A tend to accumulate in the body, while water-soluble vitamins like vitamin C don’t.
VITAMIN A
Virtually every high school biology course covers the role that vitamin A plays in vision. It helps transform light hitting the eye’s retina into electrical impulses the brain interprets as images. While that’s certainly an important part of this vitamin’s activity, it accounts for less than 1 percent of your body’s vitamin A. Its other vital roles include helping maintain the cells that line the body’s interior surfaces, boosting the production and activity of white blood cells, and directing bone remodeling. Vitamin A also helps regulate the processes by which cells split and specialize. This suggests that the body uses vitamin A to keep normal cells from turning into cancer cells and keeps cells that do become cancerous from dividing and spreading.
There are two main sources of vitamin A. Preformed vitamin A, also known as retinol, is found mainly in liver, fish oils, meat, eggs, and some vitamin supplements. The other source is fruits and vegetables rich in alpha-carotene, beta-carotene, and other so-called provitamins that your body turns into vitamin A.
Preliminary studies suggest that getting too little vitamin A may lead to a modest increase in cancer risk. They also show that once you reach a certain threshold level of vitamin A in your system, there’s no benefit in getting more. That threshold appears to be in the range of the current recommended daily intakes (see “Recommended Intake” below).
As I mentioned earlier (see page 202), getting too much preformed vitamin A may harm your bones. High intakes of retinol, the active form of vitamin A, stimulates cells called osteoclasts that break down bone. Several studies have shown that intakes of preformed vitamin A (retinol) above 1,500 micrograms (5,000 IU) increase the chances of thinning bones, breaking a hip or other bone, or getting cancer.5 Why would too much preformed vitamin A pose problems? In high amounts, vitamin A can block the effects of vitamin D, which is good for bones and muscles and has a calming effect on cancer cells.
It is easy to get too much vitamin A from supplements. I recommend avoiding vitamin A supplements unless you have a specific medical reason for them. When shopping for a multivitamin, look for one that gets all or most of its vitamin A activity from beta-carotene. Try to keep your intake of preformed vitamin A (retinol) from supplements under 2,000 IU a day.
Recommended intake: 3,000 IU for men (900 micrograms of retinol equivalents) and 2,333 IU for women (700 micrograms for retinol equivalents).
Good food sources: Food gives you either preformed, ready-to-go vitamin A or provitamin A that your body can readily convert to active vitamin A. Foods rich in preformed vitamin A—liver, fish-liver oil, eggs, and dairy products—often deliver things you don’t particularly need, like extra calories and saturated fat. Provitamin A comes from several carotenoids, including
alpha-carotene, beta-carotene, and beta-cryptoxanthin. Good fruit and vegetable sources of provitamin A include carrots, yellow squash, red and green peppers, spinach, kale, and other green leafy vegetables. The body absorbs carotenoids best if carotenoid-rich foods are consumed with some fat, like peppers or greens sautéed in olive oil.
Safety: Preformed vitamin A can harm bones at doses just above the recommended intake, and slightly higher amounts may increase the risks of some forms of birth defects. Considerably higher intakes have other serious effects. Provitamin A (from carotenoids in foods), on the other hand, is very safe. Taking in too much carotenoids can turn your skin orange, usually first noticeable in the palms of your hands, but this does not appear to have any serious or long-lasting implications.
THE THREE B’S: B6, B12, AND B9 (FOLATE)
Actually there are eight B vitamins, all of them listed on the labels on cereal boxes or multivitamin supplements: thiamine, niacin, riboflavin, pantothenic acid, biotin, B6, B12, and folate (B9). All of these help a variety of enzymes do their jobs, ranging from releasing energy from carbohydrates and fat to breaking down amino acids and transporting oxygen and energy-containing nutrients around the body. I will focus on just three of these—B6, B12, and folate—because of evidence that they may play pivotal roles in reducing heart disease and cancer.
Vitamin B6
This vitamin is actually six related compounds. They are mostly involved with breaking down protein from food into amino acids, the building blocks used to make new proteins. Taking in too little B6 causes a condition known as pellagra. Signs of pellagra include dermatitis (an inflammation of the skin), anemia, depression and confusion, and convulsions. Not getting enough B6 can also increase blood levels of homocysteine, an amino acid, which may increase the risk of heart disease (see “Homocysteine and the Heart” on page 213).
Many people take extra vitamin B6 to treat a variety of diseases and conditions, sometimes without much backing from scientific evidence. It is promoted as a remedy for premenstrual syndrome at doses far exceeding the recommended daily intake. A review of evidence suggests that 50 to 100 milligrams of vitamin B6 a day may improve the physical symptoms and depression that are part of premenstrual syndrome, but the evidence for this is weak and there is no justification for higher doses.6 Vitamin B6 has been used off and on to treat carpal tunnel syndrome. Although there’s little proof that this works, some people seem to get relief with doses of 100 to 200 milligrams.
One form of vitamin B6 helps convert the amino acid tryptophan into serotonin, an important chemical messenger used by the brain and nervous system. Because of this connection, B6 has been tested as a treatment for depression, attention deficit disorder, and other serotonin-related problems. Again, there’s no solid evidence to show whether it works or doesn’t work for these conditions.
Recommended intake: The recommended daily allowance for vitamin B6 is between 1.3 milligrams and 1.7 milligrams/day, depending on your age and sex.
Good food sources: The average American gets much of his or her daily ration of vitamin B6 from fortified breakfast cereals. Other good sources include meat, nuts, and beans.
Safety: Intakes of vitamin B6 that can be achieved only by high-dose supplements—250 milligrams/day—can cause nerve damage. The Institute of Medicine (now the National Academy of Medicine) set the tolerable upper limit for vitamin B6 at 100 milligrams/day from supplements.
VITAMIN B12
Early in the twentieth century, pernicious anemia was a grim and inevitably deadly disease. It sometimes started with paleness and fatigue, which were gradually accompanied by tingling and numbness of the arms and legs, memory loss, disorientation, and even hallucinations. In some cases, memory loss, disorientation, and hallucinations were the only symptoms. In 1934, three American researchers won the Nobel Prize in medicine for their discovery that injections of liver extract effectively treated pernicious anemia. These extracts worked because liver contains large amounts of vitamin B12, which is an essential ingredient for making red blood cells.
Today, full-blown pernicious anemia is uncommon. But getting too little vitamin B12 can still cause an array of problems, including memory loss and dementia, muscle weakness, loss of appetite, and tingling in the arms and legs. It can also lead to the accumulation of homocysteine, since vitamin B12 is involved in converting homocysteine into the amino acid methionine.
Because vitamin B12 is found only in meat and other foods from animals, deficiencies tend to crop up in vegans and strict vegetarians. In addition, as many as one in six older Americans have low blood levels of B12. For many of them, the problem isn’t a diet low in vitamin B12. Instead, it is an inability to absorb the B12 in food. (The form of B12 in fortified food or multiple vitamins can be absorbed even when B12 from food is not.) By age fifty, most of us have accumulated enough B12 and stored it in the liver to keep us going for years, even if our capacity to extract it from food declines.
People with inflammatory bowel disease or AIDS can have problems absorbing vitamin B12 from food. Drinking too much alcohol can interfere with this vitamin. So do a number of drugs, including some of the acid-neutralizing drugs used to treat ulcers; colchicine, used to treat gout; and Dilantin, used to treat seizures.
Recommended intake: The current recommended daily intake for vitamin B12 is 2.4 micrograms/day.
Good food sources: Liver is clearly the most efficient food source of B12, delivering about 23 micrograms per ounce. Other good sources include tuna, yogurt, cottage cheese, and eggs.
Safety: Although the body can handle high doses of vitamin B12—the Institute of Medicine (now the National Academy of Medicine) hasn’t set a tolerable upper limit—it’s best not to overdo it.
Folate (Folic Acid)
Folate is the natural form of vitamin B9. It is found in fruits, vegetables, and other foods (see “Good Sources of Folic Acid” on page 211). Folic acid is the synthetic version that’s used to fortify foods like bread and cereal and is the form used to make vitamins.
As described earlier in this chapter, folate helps guide the development of the embryonic spinal cord. Pregnant women who get too little folic acid increase the chance that their babies will be born with spina bifida or anencephaly. Too little folic acid also increases the likelihood of having trouble conceiving.7
Good Sources of Folic Acid
* * *
Food
Serving
Dietary Folate Equivalents*
% Daily Value**
Total cereal
3/4 cup
676
169
Chicken liver, cooked
3 oz.
476
119
Centrum multivitamin
1
400
100
Cheerios
1 cup
336
84
Lentils, cooked
1/2 cup
179
45
Spaghetti, cooked
1 cup
148
37
Chickpeas, boiled
1/2 cup
141
35
Black beans, cooked
1/2 cup
128
32
Sunflower seeds, dry roasted
11/2 oz.
101
25
Broccoli, cooked
1/2 cup
84
21
Lima beans, cooked
1/2 cup
78
20
White rice, cooked
1/2 cup
77
19
Beets, cooked
1/2 cup
68
17
Romaine lettuce
1 cup
64
16
Spinach, raw
1 cup
58
15
Orange
1 large
55
14
Wheat germ
2 tbs
53
13
Vegetable juice
1 cup
53
13
Orange juice
1 cup
47
12
Peas, frozen, cooked
1/2 cup
47
12
Baked beans
1/2 cup
46
2
Potato, russet, baked with skin
1 medium
45
11
Peanuts, dry roast
1/2 cup
37
9
Tofu, Firm
1/2 cup
37
9
* Dietary folate equivalents reflect the greater bioavailability of folic acid used to fortify foods than natural folate.
** Based on a daily value of 400 milligrams of folic acid for a 2,000-calorie-a-day diet.
Source: USDA National Nutrient Database for Standard Reference, Release 28, 2016, ndb.nal.usda.gov/ndb/foods.
Folate, along with vitamins B6 and B12, also helps the body break down homocysteine and so may help protect against homocysteine-related heart disease. A study from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston showed that, following the federal regulation that all grain products be enriched with folic acid beginning in 1998, average blood folate levels among participants in the Framingham Offspring Study (a follow-up of the famous Framingham Heart Study) more than doubled, and average homocysteine levels fell by 7 percent.8 Folic acid deficiency, defined by blood level, has almost disappeared in the United States.
Eat, Drink, and Be Healthy Page 27