Vitamin-D deficiency is linked to a long list of problems including bone weakness (osteoporosis), heart attacks, high blood pressure, cancer, diabetes, falls, muscle weakness, nervous system diseases including multiple sclerosis, psychiatric problems including depression, pregnancy problems.

After reading this list, you might think everyone should be checked for vitamin-D deficiency and be treated if low. Two circumstances are necessary to recommend this:

1. Vitamin D deficiency should cause the disease. A low level does not mean a disease is caused by vitamin D deficiency, instead, the disease may cause the level to be low.
2. Correcting the vitamin-D deficiency should improve the disease. If a low level is associated with a disease, this does not mean that correcting the low level will improve the disease.

We do know severe vitamin-D deficiency causes weak bones (osteoporosis) in adults. Having weak bones due to vitamin D deficiency is called osteomalacia.   Adequate vitamin D can prevent or improve osteomalacia. Vitamin D level may be checked in the blood. Levels less than 20 ng/ml are low. The best levels to have are controversial with most experts advising levels between 30 and 50 ng/ml. Levels this low are common. In a national survey 41.6% of people aged 20 and up had vitamin D levels below 20 ng/dl.(4) Limited sun exposure, obesity and dark skin are risk factors.

Unfortunately, there is conflicting evidence to support improvement or cure of other conditions. The Women’s Health Initiative study found calcium, plus vitamin D did not prevent heart attacks.(5) In other studies there was an increased risk.(6) Hypertension improves with correcting vitamin D deficiency with some, but not all studies.(7) Similar conflicting information is reported for cancer, diabetes, falls, muscle weakness, multiple sclerosis , depression and pregnancy. There is also conflicting evidence on the effect of vitamin D on the overall risk of dying.(8)

To prevent vitamin D deficiency, experts recommend 600-1000 International Units (IU) of vitamin D a day with 1000-1200 mg of calcium. The US Preventive Services Task Force does not recommend screening everyone. Vitamin D supplements are available as vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Many experts advise Vitamin D3 since it is more active.(5)

In summary, low vitamin D level is definitely linked to bone health. Vitamin D deficiency is associated with many other diseases. However, the relationship between vitamin D deficiency and these diseases is less established and the scientific evidence for improvement with vitamin D supplementation is unclear. The evidence shows vitamin D is needed for bone health, but it is not a proven wonder vitamin. Most people should maintain an adequate vitamin D intake with calcium in their diet or by using supplements. If needed, your physician can order a blood level.

Key References

1. US Preventive Services Task Force http://www.uspreventiveservicestaskforce.org/Page/Document/RecommendationStatementFinal/vitamin-d-deficiency-screening
2. Dawson-Hughes B: Vitamin D deficiency in adults: Definition, clinical manifestations and treatment.   http://www.uptodate.com/contents/vitamin-d-deficiency-in-adults-definition-clinical-manifestations-and-treatment?source=search_result&search=vitamin+d+deficiency&selectedTitle=1%7E150
3. Bouillon R: Vitamin D and extraskeletal health. http://www.uptodate.com/contents/vitamin-d-and-extraskeletal-health?source=see_link
4. Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res 2011; 31:48.
5. Hsia J, Heiss G, Ren H, Allison M, Dolan NC, Greenland P, Heckbert SR, Johnson KC, Manson JE, Sidney S, Trevisan M : Calcium/vitamin D supplementation and cardiovascular events., Women’s Health Initiative Investigators. Circulation. 2007;115(7):846
6. Li K, Kaaks R, Linseisen J, Rohrmann S: Associations of dietary calcium intake and calcium supplementation with myocardial infarction and stroke risk and overall cardiovascular mortality in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition study. Heart. 2012;98(12):920
7. McGreevy C, Williams D. New insights about vitamin D and cardiovascular disease: a narrative review. Ann Intern Med 2011; 155:820.
8. Bjelakovic G, Gluud LL, Nikolova D, Whitfield K, Wetterslev J, Simonetti RG, Bjelakovic M, Gluud C: Vitamin D supplementation for prevention of mortality in adults. Cochrane Database Syst Rev. 2014;1:CD007470
9. Vitamin D2 and/or D3. http://www.medscape.com/viewarticle/589256_4