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Vitamin D’s a superhero but you shouldn’t take too much

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Since you’re reading this column, we bet you’re aware that the news about vitamin D-3 — the superhero of nutrients, able to bolster bones and battle everything from heart disease to cancer — just keeps getting better. But glowing reports aren’t the whole story. And like repeat rides on the Tilt-a-Whirl at the county fair, more isn’t always better. In fact, too much D may be dangerous.

Haven’t heard much about overdoing D? You’re not alone. In the upbeat mania, that’s getting overlooked. While D’s too crucial to run low on (and many people are low), it takes some finessing to get the best results. This update’s for YOU if:

– You don’t take any D;
– You take more than 1,000 to 2,000 IU daily on your own;
– You’re considering the megadoses (as much as 100,000 IU a week) touted on the Internet;
– You’re about to plunk down cash for a D blood test that’s not from a doc.

It’s time to get this right! First, we YOU Docs believe it’s vital for you to get enough vitamin D-3. If you’re chronically short, your risk goes up for a passel of nastiness: several cancers (including breast, colon and ovarian), heart disease, osteoporosis, asthma, type 1 diabetes, multiple sclerosis and high blood pressure. New studies also are turning up links between low D and obesity in kids, digestive diseases, pneumonia, anemia and injuries among pro football players.

On the upside, researchers recently have found that having healthy amounts of D-3 relaxes your blood vessels, helps bone-building drugs work better, makes weight loss faster and easier, and even transforms slow sperm into speedy swimmers.

That’s cool. But popping lots of D isn’t your next move. Like we said, while enough is great, too much ain’t. Taking more than 10,000 IU per day, for example, might make you absorb too much D and too much calcium, causing kidney damage. (Dialysis, anyone? We thought not.) And while enough D helps bones, older women who took gigantic 550,000 IU doses every fall or winter for three to five years in one study had more fractures and more falls than those who got no extra D. Same goes for blood vessels: Too much not only nixes benefits, it stiffens your arteries.

Why can excess D double-cross you? Big doses seem to steal calcium from your bones and spew it into your bloodstream, interfering with muscle function and putting your arteries and kidneys in peril.

Aim for 1,000 IU of vitamin D-3 per day. Total. Include what’s in your multi, your calcium-D-3-magnesium tablet, your D-fortified milk or other fortified foods. Yes, we’ve seen the Internet buzz about taking super-high doses on your own. Don’t do it. The Institute of Medicine says that more than 4,000 IU per day can be harmful; we say don’t go over 2,000 IU without talking with your doc. Superpills packing 10,000 IU should be taken only under medical supervision, usually by those who don’t absorb it well or need a special regimen.

Take D-3, not plain D. It’s the most active form of the vitamin and the type your skin makes naturally when it’s exposed to sunlight for 15 minutes or so.

Get a blood test for D if: you’re dark-skinned; you’re elderly; you always wear sunscreen and a hat outdoors; you’re obese; you have trouble digesting fats; or you live north of Atlanta — during winter, the sun’s rays above there simply aren’t strong enough for you to create enough D.

What’s low? We consider D low when it’s below 50 ng/mL. While there’s little consensus on what’s definitively healthy or too high, there’s evidence that D’s dark side starts appearing above 80. Levels over 500 are toxic. Remember that D blood tests (about $35 to $40 from your doc) can give inconsistent results; recheck ultra-low or -high results.

Bottom line: Aim to hold your D levels steady between 30 and 80 ng/mL. Get tested every six months for 18 months and take the D-3 needed to get and keep you in that range (usually 1,000 IU a day; often 2,000). If you can’t get regular tests, take 1,000 IU a day. Your real age will be younger and your whole body will run better.

The YOU Docs, Mehmet Oz and Mike Roizen, are authors of “YOU: On a Diet.” Want more? See “The Dr. Oz Show” on TV. To submit questions, go to www.RealAge.com.

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