In the last fifteen years, the scientific research on vitamin D changed our perspective on this fat-soluble vitamin. Its importance goes well beyond simply preventing rickets and building strong bones. We now know that vitamin D is not simply a vitamin, but also a hormone with receptors on most cell types in the body. The presence of these receptors tells us that vitamin D plays an important role in many diverse aspects of our health instead of just the limited role it plays in bone health. The more we research, the more we find how important this nutrient is for our overall health including immune function, insulin activity, muscle function, and calcium/phosphorus balance. While recent studies debate the necessary amount of supplemental vitamin D needed, there is no debate about the importance of vitamin D to our health and that most people are deficient.
Vitamin D’s structure is similar to cholesterol and is fat-soluble, so it needs bile to be absorbed. Also known as “The Sunshine Vitamin,” because our body makes vitamin D from sunlight on our skin, vitamin D is the keeper of our blood calcium homeostasis, or balance. It regulates serum calcium, stimulates the calcification of the bone, increases absorption of calcium from the intestines, and decreases excretion of calcium from the kidneys. When our blood calcium gets too low, our parathyroid glands put out PTH. This triggers our kidneys to retain more calcium and excrete more phosphorus to create a more favorable ratio of calcium to phosphorus in our blood. Vitamin D works with PTH to assure proper balances of calcium and phosphorus in our bloodstream and in our bones.
Along with its role in calcium regulation, vitamin D also provides immune support by maintaining activated T-cell population. There are vitamin D receptors on the immune system’s macrophage and dendritic cells. Once triggered by vitamin D, the macrophage cells are capable of releasing antibacterial peptides to prevent infection. Vitamin D also regulates muscle function and composition, insulin and blood sugar, blood pressure and cardiovascular health. This amazing vitamin has also shown anticancer properties, though the mechanisms linking vitamin D to cancer prevention are not yet clear.
Diseases associated with vitamin D deficiency include at least seventeen classes of cancer like breast, colon, prostate, and melanoma. Other diseases linked to deficiency are rickets in children, MS, Autism, birth defects, chronic pain, diabetes, depression, heart disease, hypertension, IBS, muscle weakness, osteoarthritis, osteomalacia, osteopenia, osteoporosis, and PMS. From this extensive list, we can see that vitamin D’s importance in our health goes well beyond simply bone health.
What leads to vitamin D deficiency?
First, it’s important to look at the two ways to get vitamin D, diet and sunlight. Sunlight by far is the number one supplier of vitamin D, as it can be difficult to get enough vitamin D through food only. Sunlight changes the precursor of vitamin D, 7-dehydrocholesterol, into vitamin D3 (cholecalciferol). It is then transported to the liver and converted by an enzyme into 25-hydroxy-cholecalciferol (25-OHD3) and then converted into 1,25-dihydroxycholecalciferol by an enzyme in the kidneys. This final form of vitamin D is the most potent. Because of this pathway, disorders of the liver and kidneys result in impaired conversion of cholecalciferol into the more potent forms of vitamin D. Some research has shown that this decreased conversion stems from magnesium and boron deficiency. Consequently, insufficient sun exposure, specifically UVB light, can lead to vitamin D deficiency. From April to mid- October is the best time to replenish your vitamin D stores. Expose as much skin as possible to the sun midday without sunscreen for 15-20 minutes being careful not to burn. Darker skinned people may need to extend this time. For those of us living above the 35th N. latitude, we cannot get enough vitamin D during the months between October and April, so supplementation is recommended during the winter months.
Another cause of deficiency is a poor diet, including the Standard American Diet (SAD), which leaves us deficient in numerous vitamins and minerals, including D. Food sources of vitamin D sources include egg yolks, butter, cod liver oil, sardines, and dark leafy greens. Another source of deficiency is diseases that affect the parathyroid gland, liver, and kidneys all impair the synthesis of the active form of vitamin D.
What are symptoms of deficiency?
Bone pain, frequent bone fractures, and softening of the bones can be signs. Also muscle aches, muscle weakness since vitamin D helps to regulate muscle composition and prevent too much fat accumulation alongside muscle tissue. Lowered immunity can also be a symptom since a key role of vitamin D is regulation of immune response. In older persons, cognitive problems and depression can be symptoms and in children, stunted growth and severe asthma have been shown to have vitamin D deficiency as potential causes.
What does vitamin D do for you?
- Helps optimize calcium and phosphorus metabolism
- Helps prevent type 2 diabetes, insulin resistance, high blood pressure, heart attack, and stroke
- Helps prevent falls and muscle weakness
- Helps prevent osteoporosis while maintaining bone integrity
- Helps regulate immune response
- Lowers risk of excessive inflammation
- Lowers risk of some bacterial infections
- Supports cognitive function
- Supports mood stability
- Helps chronic fatigue
- Helps prevent cancer
What’s the recommended dose for supplementation?
This is a hot topic and there are many conflicting views. Recently, the recommended dosage of Vitamin D has become controversial. To maintain your current vitamin D levels, many health care practitioners recommend 1,000-2,000 IU/day. Therapeutic doses fall between 4,000 and 6,000 IU/day. Consult with your health care provider on the right dosage for you. Some experts now recommend 4,000 to 10,000 IU for therapeutic dose. A simple blood test, called 25-HydroxyD (25-OH) can test your serum level of vitamin D. Functional medicine range states the optimal range as 50-75 ng/ml. Indications for supplementation include osteoporosis, osteopenia, multiple sclerosis, cancer, autoimmune conditions, and insulin resistance. There are various ways to supplement if needed. Though vitamin D is added to fortified milk, it is as D2 which is not the most active form, so look for D3 in a high quality supplement either as pills or liquid. Fish liver oil is also a good, whole foods source available in pills or liquid.
What’s the bottom line?
The functions of vitamin D are wide and varied. We know that it is key in regulation of bone health, calcium, and phosphorus. It also regulates immune function, blood pressure, and cardiovascular health. Vitamin D helps control insulin, blood sugar, muscle composition, and muscle function. And finally, it helps prevent cancer. Lack of sun exposure and poor diet can lead to deficiency along with any diseases that affect the liver, kidneys, or parathyroid.
Vitamin D is vital to your health and eating a high-quality, nutrient dense diet may not be enough to keep optimal amounts stored in your body for all of these functions, especially if you are already deficient. Consider getting out into the sunshine 15-20 minutes a day without sunscreen during the Spring and Summer and supplementing during the colder months.
Bauman, E. Foundations of Nutrition, Micronutrient lecture, NC 106.4. Retrieved from www.dashboard.baumancollege.org.
Vitamin D Council: Understanding Vitamin D Cholecalciferol www.vitamindcouncil.org
Murray, Michael, The Encyclopedia of Healing Foods, p.100, 2005.