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A low vitamin D level is associated with higher rates of relapse and more severe disability, and higher levels are associated with higher levels of function.(1) Furthermore, low vitamin D levels are associated with higher rates of autoimmune disease, mental health problems, cardiovascular disease, and cancer.(2) For that reason I strongly urge you to monitor your vitamin D level and make getting it to an optimal range a priority.
The most natural and effective way to get vitamin D is simply to put your skin in the sun. Vitamin D is an interesting vitamin that actually acts somewhat like a hormone. We make vitamin D from cholesterol as a result of the ultraviolet radiation in sunlight hitting our skin. When this happens, the liver and kidneys transform the vitamin D into a more active form, and this allows our cells to read DNA instructions more effectively.
Unfortunately, instead of a continuous exposure to the sun the way our ancestors had, allowing a gradual increase in sunlight exposure over a season and a gradual increase in vitamin D levels and skin pigmentation throughout the summer, we spend hours inside. Think about how our Paleolithic ancestors lived and thrived. They spent most of their time outside. Although they usually slept in sheltered places, during the day they were out and about under the sun millennia before sunblock was ever invented.
We live much differently. We spend most of our time indoors. During summer, the heat and humidity in the outdoor world feels uncomfortable to us because we're not used to it and air-conditioning feels good. Even during nice weather, digital entertainment has replaced outdoor play for most people in developed societies. When we do go outdoors, our physicians – especially our dermatologists – warn us to apply sunscreen first. Of course you do not want to burn your skin, but one of the problems with sunscreen coupled with all the indoor time is that many children and most adults are still vitamin D deficient at the end of summer when our levels should be high enough to store vitamin D for the long winter.
Sunscreen blocks the frequency of light that our skin needs to make vitamin D, which is in the ultraviolet B range. The result is chronically low vitamin D levels, which increase the risk of infections, lung cancer, breast cancer, colon cancer, prostate cancer, heart disease, autoimmune problems, preterm labor, toxemia of pregnancy, schizophrenia, learning disabilities, and other mental health problems.
The lab vitamin D target range (meaning your vitamin D level as indicated by a lab test you can get from your doctor) is typically 20 nanograms per milliliter (ng/ml) to 70 ng/ml. Sometimes, it is stated as 30 ng/mL to 70 ng/mL. Because of this target range, many physicians will consider 31 ng/ml to be adequate, but with levels that low, the president still at four times the risk for autoimmune problems and cancers as someone with a higher level. The hunter-gatherer societies and those who live in the sun 24/7 have values that range between 80 and 120 ng/ml. It is likely that this is the level most consistent with optimal health.
In my clinic, we base our target range on what a breast-feeding mother needs to have enough vitamin D for her baby in her breast milk: 55 ng/ml or greater. Our target range is 50 ng/ml to 100 ng/ml total 25-hydroxy vitamin D. I tell my patients that 80 ng/ml is an ideal target. In my clinical practice, however, I find that the vast majority (more than 90 percent) are below 30 ng/ml unless they are taking vitamin D supplements, working in an outdoor job with all-day sun exposure with the arms and legs (or torso) exposed, or using a tanning bed regularly.