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By now, just about everyone has heard about the many wonderful applications of vitamin D. It helps build healthy bones, decreases insulin resistance, fights cancer, and stimulates the immune system, but some people don't get these benefits, Here's why.

If vitamin D had been invented in a laboratory, it would be promoted as a modern wonder drug. Vitamin D has an astonishing number of documented health benefits:

  • Vitamin D is essential, along with calcium, magnesium, and vitamin K, for building and maintaining healthy bones. People who get enough vitamin D are also less likely to have the falls that break brittle bones.
  • Vitamin D helps regulate the immune system, and also reinforces friendly bacteria in the digestive tract.
  • Vitamin D deficiency is associated with muscle weakness and pain, especially in the elderly.
  • Cancer, atherosclerosis, diabetes, and several autoimmune diseases all respond favorably to vitamin D, and do some forms of mental illness. Vitamin D has been found to be of benefit in conditions as diverse as hepatitis C and polycystic ovary syndrome (PCOS).

For much of the early part of the twenty-first century, it seemed that the most appropriate dosage of vitamin D would be more, more, more.

However, in 2011, British researchers reported that giving Scottish women 400 to 1000 IU of vitamin D a day failed to produce any of the expected cardiovascular benefits.

And American public health officials noticed that even in locations where vitamin D is added to food, sporadic cases of the vitamin-D deficiency disease rickets were cropping up.

What could possibly be going wrong that people weren't benefiting from vitamin D supplementation as expected? The problem turned out to be a phenomenon known as vitamin D resistance.

What Is Vitamin D Resistance?

Nutrition scientists have recognized for almost 40 years that some people just don't respond to supplemental Vitamin D, even in doses of up 120,000 IU per day, over 160 times the recommended daily allowance. In the 1970's, when the tools of molecular biology were not yet available, scientists found that resistance to high-dose vitamin D could be correlated with:

  • Magnesium deficiency. People who don't get enough magnesium can't use vitamin D.
  • Kidney problems. The storage form of vitamin D, vitamin D2 (also known as ergocalciferol), has to be converted to the active form of vitamin D, vitamin D3 (also known as cholecalciferol), by the kidneys. Early in the process of kidney failure, there can be vitamin D deficiency, even before other symptoms of renal disease are evident.
  • Biliary cirrhosis and gallbladder problems can prevent the release of bile salts that keep vitamin D dissolved in the mass of digested food in the intestines, so it can be absorbed.

Simple Solutions For Vitamin D Deficiency Don't Always Work

If you have a magnesium deficiency, the solution is simple: Take supplemental magnesium. It's inexpensive, safe, and effective. If you have a kidney problem that interferes with the activation of vitamin D2 into vitamin D3, there's an easy fix. Take supplemental vitamin D3, which is also inexpensive, safe, and effective. 

And if you have bile duct or gallbladder problems, you may also benefit from vitamin D supplements.

In some cases, however, vitamin D supplementation still does not produce the desired results. In these cases, the reason the body doesn't have enough available vitamin D even when supplements are taken is one of the most difficult of all health problems to overcome, obesity.

Continue reading after recommendations

  • K.S. Vimaleswaran et al. Causal relationship between obesity and vitamin D Status: Bi-directional Mendelian randomization analysis of multiple cohorts. PLoS Medicine. Volume 10, February 2013, p. e1001383. oi:10.1371/journal.pmed.1001383.
  • Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr. 2000 Sep. 72(3):690-3. Erratum in: Am J Clin Nutr. 2003 May
  • 77(5):1342. PMID: 10966885.
  • Photo courtesy of HealthGauge via Flickr:
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