Many of us know vitamin D as "the sunshine vitamin". It plays an important role in bone health, helping to absorb and use calcium. It also helps to maintain normal blood levels of phosphorus, another key to bone-building.
The ideal way to get vitamin D is when our body converts it to the activated form after exposure to UVB rays in sunshine. We also gain vitamin D from dietary sources and from vitamin supplements. Even by obtaining the vitamin from three potential sources, Vitamin D deficiency is common today in children and adults. In fact, more than 50% of women and men ages 65 and older in North America are vitamin D deficient, according to a consensus workshop held in 2007. People who have trouble absorbing dietary fat, such as those with Crohn's disease or celiac disease, can't get enough vitamin D from diet no matter how much they eat (vitamin D requires some dietary fat in the gut for absorption). People with liver and kidney disease are often deficient in vitamin D because these organs are required to make the active form of the vitamin, whether it comes from the sun or from food.
The discovery that most tissues and cells in the body have a vitamin D receptor and possess multiple effects on gene-regulation has provided new insights into the function of this vitamin. So far, scientists have found approximately 3,000 genes that are affected by vitamin D. Of great interest is the role it can play in decreasing many chronic illnesses including common cancers, autoimmune diseases; rheumatoid arthritis, multiple sclerosis, diabetes, infectious diseases; colds and flu, cardiovascular disease and high blood pressure.
Vitamin D deficiency can cause growth retardation, skeletal deformities and may increase the risk of hip fracture later in life. Another symptom is pain and weakness in the muscles and bones. Based on this fact, it has been suggested that some disorders diagnosed as fibromyalgia may actually be vitamin D deficiency.
A study published in the Archives of Internal Medicine in June 2008 showed low levels of vitamin D doubled the risk of death from cardiovascular causes in men and women (average age 62) referred to a cardiac center for coronary angiography. Postmenopausal women who took 1,100 international units (IU) of vitamin D plus 1,400 to 1,500 milligrams of calcium per day reduced their risk of developing non-skin cancers by 77% after four years, compared with a placebo and the same dose of calcium. The 1,100 IU dose - nearly three times the 400 IU per day recommended in federal and other expert guidelines - was correlated with a 35% higher blood level of vitamin D, on average. A large study of aging in the Netherlands published in the May 2008 issue of Archives of General Psychiatry found a relationship between vitamin D deficiency and depression in women and men ages 65 to 95.
Vitamin D Dose Recommendations
So, how much Vitamin D is enough? Based upon most recent research, the current recommendation for healthy vitamin D levels is 35 IU's of vitamin D per pound of body weight.
For a child weighing 40 pounds, the recommended average dose would be 1,400 IU's daily, and for a 170-pound adult, the dose would be nearly 6,000 IU's. However, it's important to realize that vitamin D requirements are highly individual, as your vitamin D status is dependent on numerous factors, such as the color of your skin, your location, and how much sunshine you're exposed to on a regular basis.
It is recommended you monitor your blood vitamin D levels regularly when taking oral vitamin D supplements to make sure you're staying within the optimal range. Your vitamin D level should never be below 32 nanograms per milliliter, or 32 ng/ml, and any levels below 20 ng/ml are considered serious deficiency.
The OPTIMAL value that you're looking for is 50-65 ng/ml. This range applies for everyone; children, adolescents, adults and seniors, and are based on healthy people in tropical or subtropical parts of the world, where they are receiving healthy sun exposures.
There are two blood tests that closely resemble each other: 1,25(OH)D and 25(OH)D. 25(OH)D, also called 25-hydroxyvitamin D, is the better marker of overall D status. It measures the precursor produced by the skin and converted in the body to vitamin D. This marker is most strongly associated with overall health. Please realize, however, that the "normal" lab range for 25-hydroxyvitamin D is between 20-56 ng/ml. This conventional range is really a sign of deficiency and is too broad to be ideal.
Latitude and vitamin D production in the skin
Except during the summer months, the skin makes little if any vitamin D from the sun at latitudes above 37 degrees north (in the United States, the shaded region in the map) or below 37 degrees south of the equator. People who live in these areas are at relatively greater risk for vitamin D deficiency.
Dietary Sources of Vitamin D
Vitamin D can be found in foods like milk, eggs, fish and fortified orange juice, but you only get an average of 250 to 300 international units (IU) of vitamin D per day from dietary factors alone, which is rarely enough to maintain optimal levels.
If you take a vitamin D supplement, you want to take the natural D3 (cholecalciferol), which is the same vitamin D your body makes when exposed to sunshine.
You may want to consider booking that tropical vacation. It might be exactly what your body needs!
N Engl J Med 2007;357:266-81, Michael F. Holick, M.D., Ph.D., Vitamin D Deficiency
Harvard Women's Health Watch, "Time for more Vitamin D", September 2008 issue. http://www.health.harvard.edu/newsletters/Harvard_Womens_Health_Watch
The New York Times, "A Second Opinion on Sunshine: It Can Be Good Medicine After All", June 17, 2003