Are You “D” Deficient?

Are You “D” Deficient?

Studies show that up to 90% of the vitamin D in our bodies is obtained from our skin being exposed to sunlight. Exposure to sunlight converts cholesterol in the skin to vitamin D, which is then absorbed into the bloodstream by the capillaries. As it passes through the liver, vitamin D undergoes a biological change. Continuing to the kidneys, it is converted into its active form, vitamin D hormone (calcitriol, also known as 1,25 dihydroxycholecalciferol).

Essential to Neuromuscular Functioning

Vitamin D is essential for strong bones and teeth. One way vitamin D helps is that in the body it is converted into vitamin D hormone, which improves the absorption of calcium. This is especially important in today’s aging society because 90% of the elderly who fall fracture a bone. Moderate amounts of Vitamin D can help protect against this by building bone density. A recent study showed that elderly individuals who had higher levels of the active form of vitamin D had improved muscle strength, improved protein synthesis in their skeletal muscles12 and could walk faster than those individuals with lower amounts. A meta-analysis of vitamin D and frequency of falls in healthy, elderly individuals showed that Vitamin D supplementation appears to reduce the risk of falls by more than 20%.3 German researchers found that seniors who took supplementation with either 1000 mg of calcium or 1000 mg of calcium plus vitamin D resulted in a decrease of 27% in the number of subjects with first falls at month 12 and a decrease of 39% at month 20. Additionally, parameters of muscle and neuromuscular function improved significantly.4 Vitamin D also improves balance, reaction time, and muscle strength in elderly adults56 who have fallen and had vitamin D insufficiency7 (a less significant form of vitamin D deficiency). Low levels of vitamin D, however, are associated with loss of muscle mass and vitamin D deficiency, which can lead to progressive muscle weakness and pain even in teenagers.

Vitamin D and Disease

Vitamin D also plays a significant role in improving the efficiency of the immune system. Not only does it offer some protection from autoimmune diseases,8 but studies reveal that deficiency has been associated with an increased risk of death from all causes910 and implicate it as a major risk for getting certain cancers,111213 infectious disease,1415 cardiovascular disease,16 hypertension,1718 multiple sclerosis,19 rheumatoid arthritis,20 diabetes mellitus,212223 and periodontal disease.24 Early studies have demonstrated that vitamin D supplementation can reduce high blood pressure2526 and improve the ability of cell response in non-diabetic obese individuals.27 Vitamin D supplementation also improves glucose levels in diabetic animals. Moderate amounts of vitamin D may inhibit inflammation, but excessive amounts can increase inflammation under certain conditions.

A Prevalent Problem

Vitamin D deficiency can be manifested as rickets in children (bent and soft bones) and is otherwise known as osteomalacia in adults. Recent statistics show a steady rise in the cases of rickets in the United States. Indeed, nutritional epidemiologists estimate that 50% of the population in North America and Western Europe currently experience outright vitamin D deficiency or have insufficient amounts of vitamin D.28 Vitamin D insufficiency describes the finding of biochemical evidence of deficiency without the obvious signs or symptoms.

Risk Factors for Developing Vitamin D Deficiency

  1. Limited sun exposure—
    • Since there are very few food sources of vitamin D (except for salmon, cod liver oil, and sardines), individuals who have limited sun exposure increase their risk for vitamin D insufficiency.
    • Sunscreen reduces vitamin D production in the skin by more than 95%.29 Even in sunny climates vitamin D insufficiency is common. Allow at least 10-15 minutes of exposure to sunlight before applying sunscreen during the time of day when the likelihood of sunburn is not high. If this is not possible, a modest vitamin D supplement is recommended.
  2. Breast-fed infants—Human milk often contains only a small amount of vitamin D, depending on the mother’s levels.
  3. The elderly usually have a poor dietary intake of vitamin D and limited sun exposure. They also lose up to 60% of their ability to get sufficient vitamin D from sun exposure.
  4. Dark-skinned individuals—
    • Because of increased melanin, dark-skinned individuals produce much less vitamin D from their skin than fair-skinned individuals when exposed to sunlight.
    • Forty-two percent of African American women from ages 15-49 were vitamin D deficient by the end of winter.30 Studies, published in the March 2004 issue of the American Journal of Clinical Nutrition also reported that 42% of Hispanic elderly and 84% of black elderly living in Boston were vitamin D deficient by the end of August.
  5. Individuals living in northern latitudes.31
  6. Obesity,32 stress, and chronic kidney disease can also decrease levels of active vitamin D (i.e. vitamin D hormone) in the blood.
    In order for the body to receive enough vitamin D, make sure to get adequate sunshine. If at risk for vitamin D deficiency or insufficiency, consider a modest supplementation of vitamin D within the recommended daily allowance. Be sure not to exceed the recommended daily allowance (excessive amounts can become toxic and weaken the bones).

More Advantages

Sunlight offers other advantages in addition to vitamin D. It increases serotonin, a neurotransmitter important for self-control and helps to induce sleep. Serotonin is a precursor to melatonin, a powerful antioxidant hormone, which protects the structures within the cells, increases immune efficiency, and helps to protect against cardiovascular disease.

Ultraviolet rays from the sun also kill harmful pathogens on fruits and vegetables. Under certain conditions, they reduce pro-inflammatory chemicals involved in certain autoimmune conditions. Vitamin D helps to fortify us from the influenza virus. The sun’s infrared rays improve circulation to the skin and promote relaxation.

With all these benefits, we encourage you to enjoy more of the sunny side of life by having your skin exposed to sunlight for 15 minutes before applying sunscreen and be sure to have your vitamin D level checked. Those who are at risk for developing skin cancer or have had skin cancer, should take precautions, but must have their vitamin D level checked.

This article was excerpted from Keys to Optimal Health, available from the College of Health Evangelism, online division and is used with their permission.


  1. Ceglia, L., Vitamin D and skeletal muscle tissue and function. Mol Aspects Med, 29(6):407-14, 2008.

  2. Annweiler, C., et al, Vitamin D deficiency-related quadriceps weakness: results of the Epidemiologie De l’Osteoporose cohort. J Am Geriatr Soc, 57(2):368-9, 2009.

  3. Bischoff-Ferrari, H.A., Effect of vitamin D on falls; a meta-analysis. JAMA, 291(16):1999-2006, 2004.

  4. Pfeifer, M., et al, Effects of a long-term vitamin D and calcium supplementation on falls and parameters of muscle function in community-dwelling older individuals. Osteoporos Int, 20(2):315-22, 2009, epub Jul 16, 2008.

  5. Pedrosa, M.A., Role of vitamin D in the neuro-muscular function. Arq Bras Endrocrinol Metabol, 49(4):495-502, 2005.

  6. Dehsi, J.K., et al, Vitamin D supplementation improves neuromuscular function in older people who fall,

  7. Inderjeeth, C.A., et al, Vitamin D and muscle strength in patients with previous fractures. N Z Med J, 120(1262):U2730, 2007.

  8. Adorini, L. and Penna, G., Control of autoimmune diseases by the vitamin D endocrine system. Nat Clin Pract Rheumatol, 4(8):404-12, 2008, epub Jul 1, 2008, review.

  9. Pilz, S., et al, Vitamin D and mortality in older men and women. Clin Endocrinol (Oxf), Feb 18, 2009.

  10. Melamed, M.L., et al, 25-hydroxyvitamin D levels and the risk of mortality in the general population. 168(15):1629-37, 2008.

  11. Holick, M.F., Vitamin D and sunlight: strategies for cancer prevention and other health benefits. J Am Soc Nephrol, 3(5):1548-54, 2008.

  12. Goodwin, P.J., et al, Prognostic effects of 25-hydroxyvitamin D levels in early breast cancer. J Clin Oncol, May 18, 2009.

  13. Trump, D.L., Vitamin D deficiency and insufficiency among patients with prostate cancer. BJU Int, Apr 4, 2009.

  14. Ibid, Hollick.

  15. Walker, V.P. and Modlin, R.L., The vitamin D connection to pediatric infections and immune function. Pediatr Res, Jan 28, 2009.

  16. Stood, A., et al, Vitamin D deficiency and its correlations with increased cardiovascular incidences. Am J Ther, May 15, 2009.

  17. Judd, S.E., et al, Optimal vitamin D status attenuates the age-associated increase in systolic blood pressure in white Americans: results from the third National Health and Nutrition Examination Survey. Am J Clin Nutr, 87(1):136-41, 2008.

  18. Forman, J.P., et al, Plasma 25-hydroxyvitamin D levels and risk of incident hypertension among young women. Hypertension, 52(5):828-32, 2008.

  19. Edlick, R., et al, Modern concepts in the diagnosis and treatment of vitamin D deficiency and its clinical consequences. J Environ Pathol Toxicol Oncol, 28(1):1-4, 2009.

  20. Ibid.

  21. Michos, E.D., Vitamin D deficiency and the risk of incident type 2 diabetes. Future Cardiol, 5(1):15-8, 2009.

  22. Chowdhury, T.A., et al, Vitamin D and type 2 diabetes—Is there a link? Prim Care Diabetes, Apr 21, 2009.

  23. Svoren, B.M., et al. Significant vitamin D deficiency in youth with type 1 diabetes mellitus. J Pediatr, 154(1):132-4, 2009.

  24. Ibid, Edlick, R.

  25. Lind, L., et al, Reduction of blood pressure during long-term treatment with active vitamin D (alphacalcidol) is dependent on plasma renin activity and calcium status. A double-blind, placebo-controlled study. Am J Hypertens, 2(1):20-5, 1989.

  26. Pörsti, I.H., Expanding targets of vitamin D receptor activation: downregulation of several RAS components in the kidney. Kidney Int, 74(11):1371-3, 2008, review.

  27. Nagpal, J., A double-blind, randomized, placebo-controlled trial of the short-term effect of vitamin D3 supplementation on insulin sensitivity in apparently healthy, middle-aged, centrally obese men. Diabet Med, 26(1):19-27, 2009.

  28. Shils, M., et al, (Ed.), Modern Nutrition in Health and Disease, 10th edition, Lipponcott, Wiliams, and Wilkins, 2005.

  29. Ibid, Shils, p.381.

  30. Ibid, Shils, p 389.

  31. Ibid, Shils.

  32. Wortsman, J., Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr, 72(3):690-3, 2000.

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