The two sources for Vitamin D are synthesis in the skin from sunlight exposure and food.
5-10 minutes of sunlight exposure 3 days per week will provide adequate vitamin D in many people.
There are several natural sources of Vitamin D.
These include mackerel, tuna, salmon, beef liver, cod liver oil, and egg yolks.
Milk, margarine, butter, yogurt and some brands of orange juice are fortified with Vitamin D.
There has been a significant increase in interest regarding Vitamin D during the last ten years due to the publication of studies linking low Vitamin D levels with an increased risk of cancer (breast, prostate and colon), diabetes, multiple sclerosis and heart disease.
Although the association of Vitamin D with these diseases, and their prevention with vitamin D supplementation, has not been proven via rigorous prospective clinical trials, many patients are interested in learning more about this vitamin.
Interest in Vitamin D supplementation has also increased due to potential (but still unproven in large clinical trial) benefits which include lower blood pressure in the winter, reduced susceptibility to viral infections, reduced inflammation, and reduced risk of death in elderly patients.
Vitamin D levels are influenced by age, race, vitamin D intake, age, body fat, geographic location and sun exposure.
As we age, our skin is less efficient in the production of Vitamin D.
Vitamin D deficiency is thus more common in people who are 60 years or older.
People with more skin pigmentation (darker skin) have less Vitamin D production after sun exposure.
After similar exposure to sunlight, African Americans and East Indians will have lower vitamin D levels than whites or Asians.
Thus, African Americans and East Indians may require higher levels of vitamin D supplementation to maintain adequate blood levels.
In mid-atlantic states such as Maryland, sun induced Vitamin D production doesn't occur in the late fall or winter.
Sunscreen will reduce sun-related vitamin D production.
If the lotion is applied correctly (which it often is not), sunscreen with a SPF of 8 will significantly reduce sun related vitamin D production.
Nonetheless, the potential risk of skin cancer from unprotected exposure to the sun must be carefully considered, especially given the ease with which vitamin D can be obtained as a supplement..
Vitamin D levels in the body are typically assessed by measuring 25-Vitamin D levels in the blood. Accuracy varies widely between laboratories.
Although "normal" 25-Vitamin D levels are often defined as levels of 30 ng/ml or greater, there is considerable controversy as to what defines Vitamin D deficiency and Vitamin D insufficiency.
Vitamin D deficiency is typically defined as 25-Vitamin D levels of 10 ng/ml or less. Bone abnormalities may occur if the deficiency is long-standing.
Vitamin D insufficiency is defined as 25-Vitamin D levels of 11-20 ng/ml by some and 21-29 ng/ml by others.
Although the American Association of Clinical Endocrinologists recommends goal 25-Vitamin D levels of 30-50 ng/ml, the Institute of Medicine (IOM) released guidelines in March 2011 that stated that Vitamin D levels of 20 mg/dl were "adequate for bone health in 97.5% of the population".
Serum Vitamin D levels above 50 mg/dl were described in that article as a "cause for concern".
There is considerable controversy regarding what level of D intake is required to maintain these levels, as well as what are the ideal levels for Vitamin D.
It may be that different levels of Vitamin D are required for different functions(i.e bone health vs. cancer). Optimal Vitamin D levels may also vary among people.
Some experts recommend an intake of at least 2000 IU per day in non-pregnant adults, as there appears to be no downside to this level of supplementation. This level of Vitamin D intake may be especially important in those with inadequate or irregular sunlight exposure.
The IOM however suggested a daily Vitamin D intake of 600 IU per day in adults.
They recommended that daily Vitamin D intake should not exceed 4000 IU per day, given the risk for adverse events at these levels.
Milk, yogurt, cheese, and fortified foods were recommended as the best sources of D and calcium by the IOM.
Although the IOM recommendations have not been accepted by many vitamin D experts, they provide a platform for further discussion.
The Endocrine Society released vitamin D guidelines online on June 6, 2011.
The guidelines recommend vitamin D blood levels of at least 30 ng/mL.
Due to assay variability, assays, D blood levels between 40 and 60 ng/mL were recommended for both children and adults.
At least 600 IU/day of vitamin D was recommended in adults aged 19-70 years, with a note that 25(OH)D levels consistently above the 30 ng/mL goal may require at least 1500 to 2000 IU/day of vitamin D.
Adults 70 years and older require at least 800 IU/day of vitamin D for bone health and fall prevention.
At least 1500 to 2000 IU/day of supplemental vitamin D was recommended to keep 25(OH)D levels above 30 ng/mL in this group.
Although few head-to-head trials exist, based on limited clinical evidence, D3 is preferred over D2 when selecting an over the counter D supplement.
Caution, and close medical supervision, was recommended if adult intake exceeded 4000 IU/day.
The prescription form of vitamin D is D2.
Since vitamin D is fat soluble, it should be taken with a snack or meal containing fat.
The Institute of Medicine has not released a comment on the Endocrine Society guidelines.
Given the continued controversy regarding optimal Vitamin D levels, as well as appropriate supplementation dosing, decisions regarding intake of Vitamin D should be carefully reviewed with your physician
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