Featured Nutrient: B12

Blame it on the law of unintended consequences. As soon as the food industry began to fortify foods like breads and breakfast cereals with folate, nutrition researchers found a new worry. They were concerned that people with vitamin B12 deficiencies—a hidden cause of nerve damage, depression and perhaps even mental decline in older people—might now go undiagnosed. In the past, many cases of B12 deficiency were first recognized when people developed a specific type of anemia that can be caused by either low folate or low B12 levels. Getting extra folate can mask the symptoms of B12-related anemia, making people feel fine even when levels of this crucial vitamin are low enough to cause significant nerve damage.

And then there is the antacid dilemma. B12, which is typically bound up with protein in food, is broken down by stomach acids. The widespread use of antacids for heartburn and gastric reflux has some experts fretting that the pills and liquids could block the absorption of this crucial nutrient. "At the moment we don't really know how serious that issue is," admits University of California-Davis nutrition researcher Lindsay Allen, a leading vitamin B12 expert who helped draft the current federal guidelines. Still, it's clear that a significant percentage of people aren't getting enough. According to one recent survey, 6 percent of Americans are frankly deficient; another 22 percent are borderline deficient.

What it does:

Vitamin B12 is used in making DNA, the building block of genes, and in maintaining healthy nerve and red blood cells. Early signs of trouble include fatigue and dizziness. Over time the consequences of B12 deficiency are more serious, including nerve damage, severe anemia and even dementia. Several studies have linked low B12 levels to depression. Too little may also be hard on hearts. Researchers have discovered that when B12 levels dip, levels of the amino acid homocysteine rise, which is an important risk factor for heart disease.

Older people are most likely to fall short, according to Allen. As we age, the stomach produces less gastric acid, making it harder for the body to absorb B12 from food. Between 10 and 15 percent of people over 60 are thought to be deficient. Because B12 is found mostly in meat and dairy products, some vegetarians and especially vegans may not get all they need.

How much you need:

Most experts think the current recommended daily allowance of 2.4 micrograms a day for people 14 and older provides all the body needs—although some researchers have argued that a daily intake of 6 micrograms would ensure that even people who don't absorb B12 efficiently will get enough. Luckily, it appears you can't get too much B12, as no upper limit has been set. What's more, the body effectively stores the vitamin for a couple of years. So you can fall short now and then and make up the difference later without hardship.

B12 is bound to protein, so foods like meat, fish, eggs and dairy products like yogurt and milk are the principle sources. If you're a vegetarian, it's wise to include plenty of milk, yogurt, or cheese on the menu—and to consider taking a daily multivitamin. If you're a vegan, popping a multi is particularly important. Several brands of multivitamins contain 25 micrograms of B12, more than enough to ensure that you get all you need.

Food sources of B12:

Beef liver, braised (3 oz.) = 60 mcg

Clams, baked or broiled (3 oz.) = 47 mcg

Complete Wheat Bran Flakes (1 cup) = 8 mcg

Nutritional yeast flakes (1 Tbsp.) = 4 mcg

Lobster, steamed (3 oz.) = 3 mcg

Tuna fish, light (3 oz.) = 3 mcg

Salmon, cooked (3 oz.) = 2 mcg

Beef, ground, 90%-lean (3 oz.) = 2 mcg

Milk, 2% (1 cup) = 1 mcg

Cottage cheese, low-fat (1/2 cup) = 1 mcg

Source: ESHA database 2005