WHY WORRY ABOUT LOW VITAMIN D LEVELS?
The normal range is 30.0 to 74.0 nanograms per milliliter (ng/mL).
Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation. The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol. The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol
Lower than normal levels suggest a vitamin D deficiency. This condition can result from:
- Lack of exposure to sunlight
- Lack of adequate vitamin D in the diet
- Liver and kidney diseases
- Malabsorption
- Use of certain medicines, including phenytoin, phenobarbital, and rifampin
Age | Male | Female | Pregnancy | Lactation |
---|---|---|---|---|
0–12 months* | 400 IU (10 mcg) |
400 IU (10 mcg) |
||
1–13 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
||
14–18 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
19–50 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
51–70 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
||
>70 years | 800 IU (20 mcg) |
800 IU (20 mcg) |
* Adequate Intake (AI)
Immunity
Vitamin D appears to have effects on immune function. It has been postulated to play a role in influenza with lack of vitamin D synthesis during the winter as one explanation for high rates of influenza infection during the winter. For viral infections, other implicated factors include low relative humidities produced by indoor heating and cold temperatures that favor virus spread. Low levels of vitamin D appear to be a risk factor for tuberculosis, and historically it was used as a treatment. As of 2011, it is being investigated in controlled clinical trials. Vitamin D may also play a role in HIV. Although there are tentative data linking low levels of vitamin D to asthma, there is inconclusive evidence to support a beneficial effect from supplementation. Accordingly, supplementation is not currently recommended for treatment or prevention of asthma. Also, preliminary data is inconclusive for supplemental vitamin D in promotion of human hair growth.
Mortality
Low blood levels of vitamin D are associated with increased mortality, and giving supplementary vitamin D3 to elderly women in institutional care seems to decrease the risk of death. Vitamin D2, alfacalcidol, and calcitriol do not appear to be effective. However, both an excess and a deficiency in vitamin D appear to cause abnormal functioning and premature aging. The relationship between serum calcidiol level and all-cause mortality is U-shaped, Harm from vitamin D appears to occur at a lower vitamin D level in the black population than in the white population.
Bone health
Vitamin D deficiency causes osteomalacia (called rickets when it occurs in children). Beyond that, low serum vitamin D levels have been associated with falls, and low bone mineral density.
In 2012, the U.S. Preventive Services Task Force issued a draft statement recommending that there is not enough evidence to indicate that healthy postmenopausal women should use supplemental doses of calcium or vitamin D to prevent fractures.
Some studies have shown that supplementation with vitamin D and calcium may improve bone mineral density slightly, as well as decreasing the risk of falls and fractures in certain groups of people, specifically those older than 65 years. This appears to apply more to people in institutions than those living independently. The quality of the evidence is, however, poor. And there does not appear to be a benefit to bone health from vitamin D without sufficient calcium.
Cardiovascular disease
Evidence for health effects from vitamin D supplementation for cardiovascular health is poor. Moderate to high doses may reduce cardiovascular disease risk but are of questionable clinical significance.
Multiple sclerosis
Low levels of vitamin D are associated with multiple sclerosis. Supplementation with vitamin D may have a protective effect but there are uncertainties and unanswered questions. “The reasons why vitamin D deficiency is thought to be a risk factor for MS are as follows: (1) MS frequency increases with increasing latitude, which is strongly inversely correlated with duration and intensity of UVB from sunlight and vitamin D concentrations; (2) prevalence of MS is lower than expected at high latitudes in populations with high consumption of vitamin-D-rich fatty fish; and (3) MS risk seems to decrease with migration from high to low latitudes.” A clinical trial sponsored by ChariteUniversity in Berlin, Germany was begun in 2011, with the goal of examining the efficacy, safety and tolerability of vitamin D3 in the treatment of Multiple Sclerosis.
Cancer
Low vitamin D levels are associated with some cancers and with worse outcomes in other cancers, but taking supplements does not appear to help people with prostate cancer. Currently evidence is insufficient to support supplementation in those with cancer. Results for a protective or harmful effect of vitamin D supplementation in other types of cancer are inconclusive.