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How Much Vitamin D Do You Need?


How much vitamin D is enough, and what’s the best way to get your daily dose of the so-called sunshine vitamin? It depends who you ask.

I just attended the latest Forum at the Harvard School of Public Health. The title, “Boosting Vitamin D: Not Enough or Too Much?” was a tip-off that we weren’t going to get a simple take-home message. (Watch a video of the event beginning Wednesday, March 30.)

Some background: Vitamin D isn’t really a vitamin. It’s a hormone. The body makes it when sunlight strikes the skin. This converts a cousin of cholesterol into a substance that ultimately becomes vitamin D. It is best known for helping the digestive system absorb calcium and phosphorus, so it is important for bone health. New research suggests—emphasis on suggests—that vitamin D may also be involved with regulating blood pressure, fighting cancer, and improving the immune system.

In November 2010, a panel of experts assembled by the Institute of Medicine presented its recommendation for vitamin D: 600 international units (IU) for everyone aged 1 to 70, and 800 IU for those over age 70. This was a substantial boost from the previous recommendation of 400 IU. JoAnn E. Manson, an IOM panelist, told the Forum that the new recommendations would help make sure that an estimated 97.5% of Americans were getting enough vitamin D to keep bones healthy.

Walter C. Willett and Bess Dawson-Hughes challenged that coverage, saying that the IOM’s recommendations would leave millions of people with too little vitamin D in circulation. It’s a valid concern, since a growing number of Americans don’t, or can’t, get enough vitamin D from the sun. People prone to having too little vitamin D in circulation include those who:

  • are dark skinned
  • are obese
  • don’t get outside
  • wear sunscreen or protective clothing
  • have digestive problems like celiac sprue or inflammatory bowel disease, which make it difficult to absorb vitamin D.

Willett and Dawson-Hughes say the evidence from large follow-up studies shows that taking higher amounts of vitamin D is safe and will help prevent disease.

All of the talk focused on taking vitamin D pills or fortifying food with it, not about getting it the way humans have for millions of years—from the sun. It’s a hot-button issue, since too much exposure to the sun can cause skin cancer.

So here’s my take from the Forum: If you’re between the ages of 1 and 70, get at least 600 IU of vitamin D a day, or at least 800 if you’re over 70. Food is the best way to get most vitamins, but not vitamin D. Only a few foods—salmon, tuna, sardines, milk, and fortified cereals—can give you more than 100 IU per serving. Supplements are the simplest, safest way to get vitamin D.

Being of sound mind and body, and responsible for my actions only, I also get my vitamin D the old-fashioned way. It’s a sunny afternoon, and I’m going out for a walk.

*This blog post was originally published at Harvard Health Blog*

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2 Responses to “How Much Vitamin D Do You Need?”

  1. Health Blog says:

    Thanks for the info about latest Vitamin D recommendations. I knew it as 400 IU, but did not know present recommendation is 600 IU per day.

  2. Norman Smith says:

    A blood test cannot determine the amount of stored fat-soluble vitamins or what are normal levels for these vitamins. The growing number of people with health problems for industrialized nations highlights the quality differences in the food versus non-industrialized nation. The use of petroleum-based fertilizers disrupts the microbial ecology of the land and the result is a crop that produces lower amounts of minerals and vitamins than the wild-type plant. The U.S. began using this type of fertilizer in 1913. The first sign of a problem was the dust bowl of 1933 but the decrease levels of vitamins in the food was undetected. This problem has been insidious and has increase in severity with each generation because the first dose of fat-soluble vitamins occurs in the womb and the last dose from breastfeeding thus creating a generational downward step. For perspective, there is the growing number of younger people with health problems, the need for more vaccines in children, and the heavily medicated elderly (critical low levels of fat-soluble vitamins). Tracing the molecular pathway of diseases and infections there is always one or more fat-soluble vitamins involved or the under expression of its functions. As for the debate about an inactive fat-soluble vitamin causing harm, there is no upper limit. The body regulates fat-soluble vitamins intake, metabolism, and storage. To highlight fat-soluble vitamins importance to human health, it drove evolution to develop storage cells because source is seasonal and the environmental factors are constant.

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