Are You Getting Enough Vitamin D?

Vitamin D is commonly known as the sunshine vitamin because our skin makes vitamin D in response to exposure to the sun. It was originally thought that the only problems associated with a vitamin D deficiency were a development of rickets, a softening of the bones with potential deformation in children, and osteomalacia, a softening of the bones in adults.

Today it is known that most tissues and cells of the body contain a receptor for vitamin D indicating this essential nutrient plays an important role in overall health. In fact research is starting to find vitamin D may play an important role in decreasing the risk of some cancers, autoimmune diseases, cardiovascular diseases and infectious diseases.

Measuring serum levels of 25-hydroxyvitamin D (25-OH-D) are considered the best indicator of vitamin D deficiency but the exact cutoff levels have not been determined. A vitamin D level less than 11 ng/ml (1 ng/ml = 2.5 nmol/ml) is associated with rickets. A level less than 10 to 20 ng/ml is considered to be a deficiency and inadequate for bone and overall health. A level of 21 to 30 ng/ml in considered to be a relative insufficiency and level above 30 ng/ml is considered to be sufficient for good health.

It is estimated that over 1 billion people worldwide and over half the US population has inadequate vitamin D levels (less than 30 ng/ml). Vitamin D levels below 30 ng/ml are associated with an increased risk of bone fractures, several cancers, multiple sclerosis, and type 1 diabetes. The Institute of Medicine has established adequate daily intakes of vitamin D for children and adults, but these guidelines reflect the amount of vitamin D needed to prevent rickets and osteomalacia. Also, these guidelines have not been updated to reflect the abundance of research supporting supplementation at higher doses.

The New England Journal of Medicine published an excellent review of vitamin D deficiency. The article is not free online but most public libraries should have a copy. http://nejm.highwire.org/cgi/content/extract/357/3/266

The National Institutes of Health has a good overview of vitamin D but they still have the old intake guidelines. http://ods.od.nih.gov/factsheets/vitamind.asp

An important issue was raised in the American Journal of Clinical Nutrition in March 2007. The author states the press has been effectively reporting the prevalence of vitamin D deficiency as research has come out. The problem comes when the media has been referencing the outdated guidelines as the correct way to supplement vitamin D intake. In fact the suggested 400 IU dose from the outdated guidelines will only raise vitamin D levels by 2.8 to 4.8 ng/ml. The author states a dose of 1700 IU per day would be needed to raise blood levels enough. This is about 4 times the dose. http://www.ajcn.org/cgi/content/full/85/3/649

The Linus Pauling Institute at Oregon State University has a great review of the literature and has published their own set of guidelines for Vitamin D intake. They say generally healthy adults should take in 2000 IU of vitamin D daily. http://lpi.oregonstate.edu/infocenter/vitamins/vitaminD/

A group of 18 scientists at the University of California have joined together to support a total daily intake of 2000 IU of vitamin D. They want the government to re-examine its recommendations and build awareness of the deficiency problem. http://newsroom.ucr.edu/cgi-bin/display.cgi?id=1968

What about Toxicity?

The National Institutes of Health (NIH) has published tolerable upper limits for vitamin D intake of 1000 IU a day for the first year of life and 2000 IU a day for everyone else. At the same time the NIH reports many scientists challenge this upper limit due to newer evidence stating doses as high as 10 000 IU per day are reportedly safe. Because of this, the NIH upper limits may be overly conservative.

Vitamin D toxicity can cause nausea, vomiting, poor appetite, constipation, weakness and weight loss. It can also raise calcium levels causing confusion and heart rhythm abnormalities. Also, the combination of vitamin D and calcium intake can increase the chance of kidney stones. A serum level of greater than 200 ng/ml is considered to be toxic.

The Bottom Line

Most people should probably increase vitamin D intake. The Linus Pauling Institute recommendation of 2000 IU per day is probably safe. It falls right at the NIH upper limit of safety which are considered to be very conservative. Vitamin D is available in many pharmacies in doses of 400 IU and 1000 IU. Vitamin D is also found in fortified milk and other foods. It also occurs naturally in fatty fish and egg yolk. If your diet includes a lot of these foods, consider supplementing with 400 to 1000 IU of vitamin D. Otherwise you may consider supplementing with 1000 to 2000 IU daily of vitamin D. Check with your doctor, especially if you have kidney disease, hyperparathyroidism, sarcoidosis, tuberculosis or lymphoma. These conditions may cause an excessive increase in calcium levels in response to vitamin D.

When selecting a product, chose one that states it contains vitamin D3. This is the active form more easily utilized by the body.

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