Vitamin D: How Much More? New Study Raises Dosage Questions

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A much anticipated new study on guidelines for vitamin D and calcium consumption raised recommended intake levels for both nutrients in regard to bone health but advised more research on other potential benefits, such as heart health and depression prevention.

The Dietary Reference Intakes for Calcium and Vitamin D report was released by the Institute of Medicine (IOM), the health arm of the National Academy of Sciences, on November 30, 2010. The IOM was asked by the United States and Canadian governments to assess the current recommended dosages for North Americans and review scientific literature to date in order to update the widely used Dietary Reference Intakes (DRI) used for nutrition labels and school lunches, as well as by doctors and nutritionists.

The report made front-page news across the country, but many headlines were confusing and even contradictory: Stop taking so many vitamin D supplements? Or take more? The bottom line was that the DRI for vitamin D were sharply increased, but less so than many experts anticipated. The report also concluded that most people have sufficient D levels in their blood for bone health (emphasis added), contradicting other reports that vitamin D deficiency is widespread.

Our bodies make enough vitamin D to last a few days when sufficiently strong sunlight shines on exposed skin (equivalent to face, arms, and shoulders) for about 15 minutes. Until vitamin D was added to milk in the 1930s, and more recently to some orange juices and cereals, salmon and other fatty fish were the only nutritional sources available (for more on vitamin D, see last January’s Almanac).

Both vitamin D and calcium have been often in the spotlight over the past decade. Vitamin D in particular has been written up frequently, as numerous studies have shown links between higher levels of D in the blood and reduced risk of cancers, heart disease, depression, and other health problems.

The new report conservatively states: “Scientific evidence indicates that calcium and vitamin D play key roles in bone health. The current evidence, however, does not support other benefits for vitamin D or calcium intake.” In other words, the new guidelines are based on the amount of vitamin D required to keep levels adequate in the blood to ensure bone health. Although there is mounting research that vitamin D, which is actually a hormone, plays many other critical roles in the body, the IOM decided more evidence was required before making official dosage recommendations for, say, optimal heart health.

So what are the new DRIs for vitamin D?  (given in IU, or international units)

Age New DRI Old DRI
1-70 600 UI 200 UI
70+ 800 IU 400 IU

Upper Intake Levels  (the safe total intake levels)

9+ 4,000 IU 2,000 IU

Although the DRI for most people tripled, they are still less than the daily 1,000–2,000 IU some experts have recommended. Remember that the report refers to the general population, and not individuals, so your doctor may have different recommendations based on your health.

The IOM also raised the Upper Intake Levels for vitamin D from 2,000 IU to 4,000 IU for ages 9 and above. Although doubled, this level remains well under the 10,000 IU or more some experts believe are safe. While no studies showed harm for daily doses below 10,000 IU, the IOM was concerned that certain “risks may increase” above 4,000 IU. There is no danger of making too much D from the sun, as the body easily regulates the amount absorbed from the skin, but the upper limit does matter for people taking supplements.

So, how much vitamin D should you be taking? It is always best to check with your doctor. You can also let the sun guide you. If you are fair-skinned and expose your arms and face without sunscreen for at least 15 minutes most days during the sunnier months (roughly April through September), you probably don’t need supplements during those months. During the rest of the year, or if you stay mainly indoors or have darker skin, monitor your dietary intake* of vitamin D to ensure you’re getting your DRI. If you choose to supplement, consider how much D you get from your food and regulate your supplements so that your total intake remains below 4,000 IU.

*The World’s Healthiest Foods website has the amounts of vitamin D in the few whole foods that naturally contain it. Just add these to the D in any D-fortified foods (milk, some OJ, and some cereals) you eat, and that will give your total dietary vitamin D intake.

- Rebecca Taggart

Not intended as health/medical advice. Always consult your healthcare professional before starting a new diet or exercise regime.

 

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