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Q: Is it true that a vitamin A overdose is dangerous?
A: Three studies have shown that people taking too much vitamin A had a higher risk of lung and liver cancers, atherosclerosis (hardening of the arteries) and, for smokers, stroke. It also weakens your bones. So keep your A supplement under 2,500 IU daily (if you are pregnant, ask your doctor how much to take).
Q: I think I might have a vitamin B12 deficiency, but how can I find out? What should I eat or take if I need more?
A: To know for sure, your doctor can order a blood test to measure your level. A vitamin B12 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervous system. At levels only slightly lower than normal, symptoms such as fatigue, depression and poor memory may emerge, although these symptoms by themselves are too nonspecific for a diagnosis. A somewhat greater vitamin B12 deficiency can cause loss of position sense—and balance—not knowing where your legs are in relation to you. A severe deficiency can cause loss of pain and temperature sense, mania and psychosis.
A multivitamin should provide enough B12; we believe almost everyone should take half of a multivitamin twice a day as insurance against an imperfect diet. Foods rich in B12 include salmon, tuna, hamburger, lamb, bran and wheat flakes. Deficiencies are most common in strict vegans.
Q: A friend takes vitamin C to ward off colds and says it’s also good for the skin. Is this true?
A: Vitamin C is a proven weapon against colds and, if used at night on your skin, helps keep it looking young.
You have to be realistic about colds, which are an incurable, unavoidable trade-off of human interaction—talking to people, shaking their hands, sharing subway poles. Germs spread as we cough, blow, sniff and sneeze, and most American adults catch two to four colds every year.
But you can speed up the course of a cold. Chicken soup, zinc lozenges and vitamin C have proved to shorten a cold’s duration from five days to three if you act quickly. Pick one tactic and take regular doses for two or three days, starting when you first feel symptoms. That’s 500 milligrams of vitamin C four times each day with plenty of water (in addition to your one-half of a multivitamin twice daily) or one zinc lozenge every six hours or a cup of chicken soup four times a day.
Q: My blood test from a physical revealed a vitamin D deficiency. How could I have this and not know it? Why is it important to correct?
A: You can’t feel a vitamin D deficiency, which can lead to long-term problems such as cancer, heart disease, depression and bone thinning. (Vitamin D3 is essential for calcium absorption and incorporation into bone.) Studies have found that 50 to 87 percent of Americans are short of vitamin D. Take what is needed to get (and keep) D at its normal level, which means you must measure it again.
Much of what we do and use for our health boils down to protection: helmets to protect from brain injury, shoes to protect feet from sharp objects, and aspirin to protect us from arterial aging as well as colon and breast cancer. You can’t buy what is perhaps the greatest protector: the TP53 (TP stands for tumor protein) tumor suppressor gene, which recognizes when your cells are at risk of developing into cancer and marshals your defenses. It’s a biological guard dog that senses a tumor threat and then regulates the proteins that cause cancer when mutated.
And one form of vitamin D—D3—helps make the building blocks critical for healthy functioning of the TP53 gene. We don’t know exactly how it works. One theory is that a form of vitamin D is toxic to potentially cancerous cells. A second theory is D bolsters the capabilities of the TP53 guard dog to sniff out cancerous cells and mount a counterattack. Either way, we recommend starting with 1,000 IU of vitamin D3 a day if you are 60 or younger and 1,200 IU if you’re older than 60. You can take it in an inexpensive supplement form.
You also can get vitamin D through sunlight. Spending 10 to 20 minutes outside if you live south of a line between Atlanta and Los Angeles should boost your levels but increases skin cancer risks, so we strongly advise you to get your vitamin D3 through food and a supplement and to wear SPF 45 sunscreen every time you go out—even if the sun isn’t shining. (If you live north of Los Angeles and Atlanta, the sunlight doesn’t have enough energy between Oct. 15 and April 15 to make active vitamin D.)
Q: Should I take a vitamin E supplement each day? I’m a 37-year-old male with a moderately active lifestyle.
A: The multivitamin we mentioned previously gives you enough vitamin E; many contain 30 IU. Overdoing E is risky: A big new cancer study found that taking 400 IU of E daily raises prostate cancer risks 17 percent. And substances that increase prostate cancer often are found to increase breast cancer in women, and vice versa, so we advise women to limit vitamin E, too. Food isn’t a worry unless you eat nothing but almonds, sunflower seeds and spinach (unlikely!).