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THE RISK OF TOO LITTLE VITAMIN D
Researchers may be worried about high doses of folic acid and selenium, but when it comes to Vitamin D, they worry that we're getting too little. "The vitamin D studies are all coming back with good news," says Reinhold Vieth, a professor of nutritional sciences and of laboratory medicine and patho-biology at the University of Toronto. Vieth is one of a growing number of experts who argue that the current Recommended Dietary Allowances for vitamin D should be higher. The RDAs for adults range from 200 IU (if you're 50 or younger) to 600 IU (if you're over 70). Most multivitamins have 400 IU (the RDA for people to 70). "I flat-out recommend that people take 1,000 IU a day all the time," says Vieth. "There's no downside."
BONES & MUSCLES
The strongest evidence for higher intakes comes from trials that gave older people vitamin D (often with calcium) to prevent bone fractures or falls or to boost muscle strength. "Trials that gave people only 400 IU a day did not show an effect," says Bess Dawson-Hughes, director of the Bone Metabolism Laboratory at the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University. "Trials that had positive results gave people bigger doses."
How much vitamin D is enough?
"For the average older person, it's 800 to 1,000 IU a day," says Dawson-Hughes, who is past president of the National Osteoporosis Foundation. "That's the average amount needed to get the 25 hydroxy vitamin D blood level up to 75 nanomoles per liter."
That's the level that lowers the risk of breaking a hip or other bone (but not the spine, which isn't affected by vitamin D). "It's the ballpark minimum for improving muscle performance and preventing falls," adds Dawson-Hughes.
It's easy to see how vitamin D could prevent fractures. Researchers have long known that it boosts bone mineral density, in part by helping the body absorb calcium from foods.
But muscle? "Biopsies show enlarged fast twited muscle fibers in people who are treated with vitamin D," explains Dawson-Hughes.
Stronger muscles helps explain why trials have found a 35 percent lower risk of falls in older people who are given 800 IU a day of vitamin D. But that's not the whole story.
"Vitamin D may be affecting balance because we know it has effects in the brain," suggests Dawson-Hughes. "There are vitamin D receptors just about everywhere you look in the brain."
Vitamin D's impact on bone and muscle is backed by the strongest evidence and that's enough to recommend that people take 1,000 IU a day. Studies examining the vitamin's impact on other diseases are coming fast and furious.
A month doesn't go by without new reports that Vitamin D may lower other risks:
• Cancer. There's some evidence that people with higher blood levels of vitamin D have a lower risk of cancers of the breast and prostate. But overall "there's more evidence for colon cancer."
Men in the Health Professionals Follow-Up Study and women in the Nurses' Health Study who had higher blood vitamin D levels in 1993 had roughly half the risk of colon cancer over the next 8 to 11 years than those with lower blood leve1s.
But in 2006, the Women's Health Initiative reported that the roughly 18,000 women who were randomly assigned to take vitamin D (400 IU a day) for seven years had no lower risk of colon cancer than the 18,000 who took a placebo. End of discussion? No.
"The dose wasn't high enough and people weren't taking their pills enough," says the University of Toronto's Reinhold Vieth. Virtually all of the women had blood vitamin D levels lower than 75 nanomoles per liter (nmol/L). In fact, when researchers looked at all the women, whether they were told to take vitamin D or the placebo, those with levels under 31 nmo1/L had 2 ½ times the risk of those with at least 58 nmo1/L.
"There was a substantial reduction in colon cancer as blood levels of vitamin D went up," Vieth notes. But the drop wasn't related to whether women were told to take vitamin D, he adds, because "the dose was trivial and people weren't compliant enough."
• Diabetes. After reviewing a number of studies, experts estimated that people with higher blood levels of vitamin D had a 64 percent lower risk of diabetes than people with lower levels.
"Vitamin D is needed for optimal insulin secretion," says Tufts' Bess Dawson-Hughes. "And vitamin D may influence responsiveness to insulin."
• Periodontal disease. When researchers used probes to poke around more than 77,000 teeth in 6,700 people aged 13 to 90, the gums of those whose blood vitamin D levels averaged 100 nmol/L were 20 percent less likely to bleed than the gums of those whose levels averaged 32 nmol/L.
"The evidence on gingivitis and tooth loss suggests that vitamin D influences oral health by decreasing inflammation," explains Dawson-Hughes.
In a trial that gave 145 older people a placebo or 700 IU a day of vitamin D enough to raise their blood levels from 71 to 112 nmo/L the vitamin D takers had 60 percent lower risk of tooth loss..
• Mental function. A few small studies have suggested that low vitamin D blood levels are linked to poor scores on thinking and memory tests. ''It's looking like low vitamin D contributes to poor mental function in the elderly," says Dawson-Hughes.
• Arthritis. In 1996, researchers reported that people who had osteoarthritis in their knees were three times more likely to get worse if they had low blood vitamin D levels. But a recent study didn't find a link.
"There's a large vitamin D trial at Tufts to see what happens to osteoarthritis of the knee," says Dawson-Hughes. Scientists are putting 144 people with arthritis in their knees on either vitamin D (2,000 IV a day) or a placebo for two years.
• Multiple sclerosis. When researchers compared blood vitamin D levels of 257 Army and Navy recruits who were diagnosed with multiple sclerosis to the blood levels of 514 recruits who remained free of the disease, the risk of MS was 62 percent lower in those with the highest vitamin D levels (they averaged 99 nmoI/L).
"There's research on a number of autoimmune diseases, but so far, multiple sclerosis is the most highly linked to vitamin D," says Dawson-Hughes.
Why would one vitamin affect so many systems?
"A lot of different tissues have the ability to make the Vitamin D hormone because it's a signaling molecule, The quality of communication between cells is determined by the vitamin D because it's the raw material for the message ",explains Vieth. In contrast, there's no shortage of raw material to make other hormones.
"Testosterone and estrogen are made from cholesterol, which E circulates in the bloodstream in abundance, so you don't have to worry about supply," says Vieth. "Circulating levels of cholesterol are about 5 million nanomoles per liter but for vitamin D, they're about 100 nanomoles per liter."
"If you're talking about vitamin D toxicity, you're talking about gross excess," says Vieth. "I tend to be pretty blase about vitamin D toxicity because it has always been industrial scale goof-ups when somebody makes a mistake and adds a milligram instead of a microgram to foods or supplements."
Vieth recently gave mega-doses ranging from 4,000 to 40,000 IU a day of vitamin D to 12 patients with multiple sclerosis. After 28 weeks, their blood levels rose to an average of 386 nmol/L, but extensive blood tests found no problems. "We raised the vitamin D to very high levels and nothing happened," says Vieth.
It's easier to get 1,000 IU of vitamin D from a supplement than from fortified foods or from sunlight. Vitamin D only causes toxicity if it raises levels of calcium in the blood.
THE BOTTOM LINE
Shoot for a total of 1,000 IU a day of vitamin D3 (cholecaliferol) from your multivitamin plus an extra vitamin D supplement combined. Vitamin D2 (ergocalciferol) is only about half as potent.
If you want to know your blood vitamin D level, make sure your doctor tests 25 hydroxyvilamin D. The levels should be at least 75 nmol/L (or 30 ng/l) and ideally 9010100 nmol/L (361040 ng/l).
"But for that to happen, you have to saturate all the vitamin D carriers in the bloodstream," explains Vieth. "Less than one-fortieth of the carrier proteins are normally occupied, so you have to throw in huge excesses to overwhelm the system."
Could vitamin D have some unexpected adverse effect at lower doses?
A study of Finnish smokers in which men with higher blood levels of vitamin D had a higher risk of pancreatic cancer. But those results might not apply to non-smokers. A study of 46,000 U.S. men and 75,000 U.S. women found that higher vitamin D intakes were linked to a lower risk of pancreatic cancer. "Vitamin D levels go up and down in Scandinavia," notes Vieth.
Studies show lower overall cancer rates and death rates in people with higher vitamin D levels in their blood. Vieth has urged the National Academy of Sciences' Institute of Medicine to raise the Upper Level- the highest safe dose to take regularly for Vitamin D. "The IU should be 10,000 IU, rather than the current 2,000 IU," he contends. In the meantime, says Vieth, taking 1,000 IU a day would raise the average person's blood level of vitamin D to 75 nmol/L.
"Forget cancer, forget everything-the evidence on bone alone directs people to get 1,000 IU a day," he argues. "How many reasons do you need?"
5 Ways Vitamin D Could Save Your Life
Vitamin D is known as the sunshine vitamin and it has a lot of sunny benefits, but most Americans aren't getting enough of it.
Between 50 percent and 75 percent of Americans get suboptimal levels of vitamin D, according to a study published in the Archives of Internal Medicine.
A committee at the Institute of Medicine is meeting to determine whether the recommended daily intake of vitamin D should be increased. ABC medical contributor Dr. Marie Savard came on "Good Morning America" today to offer five ways vitamin D can aid your health and tell you how to get more of it.
Why People Are Vitamin D Deficient
Nature gave us only one good source of vitamin D, and that is the sun. We are meant to absorb vitamin D from the sun through our skin.
When we lived closer to the equator and worked outdoors, we were OK. But that is not the case today. And food is not a good source of vitamin D, not even fortified food.
Five Ways Vitamin D Can Save Your Life
Five Ways to Get Vitamin D
Vitamin D-3 (400 IU - 60 Tablets)