Now that I know what vitamin D is and why it's important, how much should I consume?
The federal government sponsored Institute of Medicine (IOM) currently recommends an Adequate Intake (AI) of 200 International Units (IUs) for adults under age 50, 400 IU for those 51-70 and 600 IU for adults age 71 and over. Some physicians recommend 600 IUs for women 51 and older, because of their increased risk of osteoporosis. However, these recommendations are several years old and as research about vitamin D increases, there is a growing body of scientists and physicians who believe that the daily intake should be increased greatly. Some recommend 1,000 IU daily, while some suggest taking in 10,000 IU daily. While, there is no consensus on how much vitamin D it takes to cause toxicity, ten thousand IU is currently the upper intake limit. While this sounds like a tremendous amount, fair skinned people can manufacture as much as 15,000 IU or more in just 30 minutes of optimal sun exposure.
Since the ongoing debate about optimal intake and calls by leading scientists for the IOM to revise and update their recommendation for Adequate Intake of vitamin D, the National Institute of Health, Office of Dietary Supplements (ODS) has been working with other federal agencies to learn more about vitamin D. Also, a new revised "Dietary Guidelines for Americans" is due to be published in 2010 and may include new recommendations for vitamin D, depending on the results of the government's research.
Ultimately, you should consult your doctor to find out whether you are at risk of being vitamin D deficient (determined through a blood test) and how much your doctor believes you should consume. Post-menopausal women and people with osteoporosis may need to take more than the average person, because of calcium deficiency.
What are sources of vitamin D?
There are three main sources of vitamin D: food, sunlight and supplements.
Food: Food that is naturally rich in vitamin D isn't very common. Among natural sources, cod liver oil is the best at 1,360 IU per tablespoon (mostly in D3 form- the most readily absorbed form). Salmon and mackerel come in second with between 345 and 360 IUs per 3.5 ounce serving. Also, wild Alaskan salmon may have more as much as 25% more vitamin D than farmed salmon, possibly because the farmed salmon feed is fortified with D2, the less readily absorbed type of vitamin D. Three ounces of non-white, oil packed tuna contains 200 IU. It is also found in anchovies. One egg contains 20 IU and 3.5 ounces of beef liver contains 15 IU. There may be other sources in meat, but it has not been thoroughly studied.
Since many people don't eat enough fish and eggs to meet the daily requirements, many foods are artificially fortified with vitamin D. This is especially true with dairy products, since vitamin D is key to our ability to absorb the calcium in dairy. Almost all milk sold in the U.S. is fortified with 100 IU per 8 oz. serving in the D3 form. Some yogurts, cheeses, cereals, breads and juices are also fortified. You can even buy calcium and vitamin D-fortified orange juice!
Sunlight: Your body produces vitamin D when your skin absorbs ultraviolet radiation from the sun and it produces more and more quickly than you can ingest through meals. Fair skinned people can manufacture as much as 15,000 IU or more in just 30 minutes of optimal sun exposure.
However, here are some important things to remember about "optimal sun exposure." First, the sun needs to be higher than 45 degrees above the horizon in order to adequately produce vitamin D, so Noon is the optimal time of day. Secondly, where you live plays an important factor. For anyone above 35 degrees latitude (think North Carolina to California) the sun shines at such an angle that its rays aren't strong enough to cause vitamin D production for at least one month a year. Third, people with darker skin pigmentation require longer exposure time than fair skinned people. Fourth, as we age, the skin's ability to produce vitamin D diminishes, so older people require more time in the sun. And finally, sunblock eliminates most of our ability to produce vitamin D. SPF 8 blocks 98% of the UV rays needed for the transformation. People need to balance their concerns about sun exposure and the risk of developing melanoma with the benefit of sun exposure for producing vitamin D. 10-15 minutes two to three days a week in the mid-afternoon should be plenty of exposure for vitamin D production. (People with RA who take methotrexate should take extra care, though, because of the increased risk of developing melanoma -- the deadliest form of skin cancer.)
Supplements: Supplements are a way to make sure intake of vitamin D is adequate, especially if one needs to limit sun exposure or doesn't receive enough from dietary sources. Most daily multivitamins contain 100% of the current recommended AI (400 IU) for people up to age 70. They are also made using the D3 form, which is the most readily absorbable. Some multivitamins contain as much as 1,000 IU.
Published On: July 21, 2008