Vitamin D is totally one of those hyped nutrients; everyone talks about it all the time as an essential vitamin for health (and part of why I’ve started this series is to remind everyone that *all* vitamins and minerals are essential!!). But, does vitamin D deserve this reputation? Actually, yes!
Vitamin D, also named cholecalciferol, is truly deserving of its reputation as a supernutrient. It is an incredibly vital vitamin SLASH hormone SLASH transcription factor (controls genetic expression) that is critical for numerous bodily functions. Like, thousands of functions!
Unlike some other vitamins and all minerals, we are able to make our own vitamin D: with exposure to sunlight, of course! But, just how is this vitamin made? First, specialized skin cells are activated when we expose our skin to UVB waves (by going outside and enjoying some sunlight on bare skin). After it’s synthesized in the skin, the inactive form of vitamin D must travel to the liver, where it’s further modified, and then is activated by the kidneys (so people with liver or kidney disease often have low vitamin D!). From here, vitamin D can work its magic all over the body.
We can also get vitamin D from foods! The RDA for adults is 600 IU/day, though it’s important to note that we can store vitamin D in the liver (during the winter months, for example). But, we can get vitamin D from more than just the sun – did you know that the foods richest in vitamin D are Paleo staples? That’s right, the foods highest in vitamin D are pink salmon (465IU/serving), mackerel (211IU/serving), sardines (164IU/serving), and egg yolks (37IU/serving).
As I mentioned before, vitamin D is a steroid hormone that controls expression of more than 200 genes and the proteins those genes regulate. The vitamin binds to vitamin D receptors, called VDRs, on the nuclear envelope of cells. Thousands of receptors have been identified! Vitamin D is also essential for mineral metabolism. Specifically, it helps to maintain appropriate calcium balance in the blood. It achieves this by working with the parathyroid gland to determine how much calcium will be deposited or excreted from bones as well as by modifying the amount of calcium that is excreted by the kidneys and how much is absorbed in the gut during digestion. This function operates in parallel to phosphorous metabolism, which is also regulated in part by vitamin D.
Vitamin D is also crucial for regulating several key components of our immune system, including formation of important antioxidants. Very importantly, Vitamin D has recently been shown to modulate inflammation and may be critical in preventing and/or treating autoimmune and inflammatory diseases!! Conversely, inadequate vitamin D levels have been repeatedly associated with inappropriate immune responses, demonstrating this vitamin’s essential value in maintaining healthy immunity. Vitamin D is also involved in the biosynthesis of neurotrophic factors, regulating release of such important hormones as serotonin (required not only for mental health but also for healthy digestion!) and insulin. Vitamin D helps control cell growth, so it is essential for wound healing. Scientists continue to discover new ways in which Vitamin D is essential for human health; for example, Vitamin D may prevent cancer.
Severe vitamin D deficiency is called rickets, in which the bones of infants and children fail to mineralize. Deficiency in adults might manifest as osteomalacia or muscle weakness and pain. Many factors, including sun practices, breast feeding, diet, clothing style, and geographical location, impact someone’s risk for vitamin D deficiency.
About 75 percent of Westerners are deficient in vitamin D. Optimal serum vitamin D levels are between 50 and 70 nanograms per milliliter (ng/mL). It’s important to ask your healthcare provider to test your levels. If you’re deficient, it can be tough to get enough vitamin D3 from sun exposure and foods, so consider supplementing with vitamin D3 (5,000 IU daily is a standard dose to address deficiency but ask your healthcare provider for a recommendation based on your personal health history) and recheck every three months to make sure you don’t overshoot the mark. Vitamin D levels in excess of 100 ng/mL can also cause health problems.
Vitamin D production from ultraviolet light exposure is not the only important aspect of sun exposure. Cells throughout the body, including the skin and eyes, are sensitive to blue light from the sun, which is strongest in the morning. When special cells in the retina of the eye are stimulated by sunlight, they directly affect the pituitary gland and the hypothalamus region of the brain. The hypothalamus is responsible for circadian rhythm (our body’s internal clock) and regulation of hormones and the nervous system. Proper regulation of circadian rhythm is crucial for quality sleep, stress management, and the cyclic pattern of expression of so many hormones in the body. One important circadian rhythm hormone, produced by the brain’s pineal gland and regulated by sunlight, is melatonin. In addition to being critical for quality sleep, melatonin is a powerful antioxidant, is important for intestinal function, and can help prevent depression. The hypothalamus and the pituitary gland influence the adrenal glands, which control cortisol production. These important effects on brain activity, which increase alertness, improve cognition, and boost mood and vitality, are all independent of Vitamin-D production. So, while taking a Vitamin-D3 supplement is very helpful when the sun is scarce in the winter months (or if you do shiftwork or face other challenges to getting out into the sun), it can’t replace the huge range of health benefits of just plain old getting outside. See also Fructose and Vitamin D Deficiency: The Perfect Storm?, Why Sun Exposure Is So Important, and Regulating Circadian Rhythm (and why that’s important)
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Grober U, Spitz J, Reichrath J, Kisters K, Holick MF. Vitamin D: Update 2013: From rickets prophylaxis to general preventive healthcare. Dermatoendocrinol. 2013;5(3):331-347.
Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911-1930