While referred to as both a vitamin and pro-hormone, to declare that vitamin D is critical for one’s health is an understatement. Virtually every cell in our body contains a vitamin D receptor, which when activated, vitamin D binds to these sites influencing the expression of over 1,000 genes. As I mentioned in a previous post, gene expression/regulation basically gives our cells control over their structure and function (actions). Our genes can not control themselves on their own, rather they must interact with and respond to an organism’s environment. Here enters the magnitude of risk our daily diet and lifestyle choices pose to our own human health as well as to the health of future generations.

Unlike other vitamins, which are vital nutrients that must be obtained through diet and/or supplementation, vitamin D is synthesized in our bodies when our skin is exposed to sun (specifically UVB radiation). Our skin does not actually contain vitamin D but rather a cholesterol containing precursor which kick starts the process of converting Vitamin D into the active form our bodies require. Vitamin D then follows a metabolic pathway through the liver and kidneys to become active (vitamin D obtained from food or supplements follows this same pathway).

Vitamin D is fat-soluble which means fat should be present for absorption when we obtain it from our diets. Also when in our bodies, vitamin D is stored in fat tissue as well as our liver.  Vitamin D not only promotes the absorption of calcium in our intestines but it tightly regulates the levels of calcium and phosphate in our blood, promoting the mineralization and growth of bones and preventing the calcification of excess calcium in our arteries, joints, tissues, brain and organs. This mechanism ultimately protects us against conditions such as osteoporosis (reduced bone density), bone fractures and coronary artery disease. In addition to calcium and phosphorus, vitamin D works synergistically with vitamin A, vitamin K2, magnesium and zinc. For example, if an individual has high levels of vitamin D but is deficient in vitamin K2, he/she is at an increased risk of soft tissue calcification. While vitamin K1 is mostly found in leafy greens, animal products as well as natto (a fermented soy product) are the best sources of vitamin K2. In fact, organ meats (mainly liver), full fat grass-fed dairy and pasture raised egg yolks are among the best sources of this commonly overlooked nutrient. It should be noted that bacteria in our intestines can also synthesize vitamin k2, however, this mechanism does not appear to be sufficient in preventing deficiency.

Ongoing research and findings: There is a considerable amount of research associating vitamin D deficiency with several autoimmune disease including multiple sclerosis, rheumatoid arthritis, fibromyalgia, type 1 diabetes and systemic lupus erythematosus (SLE). Epidemiological studies also suggest links between deficiency and several cancers, including breast and colorectal. Vitamin D is also found to play a crucial role in thyroid hormone metabolism. In fact, many individuals suffering from hypothyroidism are commonly found to be deficient regardless of sun exposure.

However, do keep in mind that more does not necessarily mean better. In fact, vitamin D follows a U-shaped curve, meaning that both low and very high levels are associated with negative health outcomes (i.e. heart attacks, strokes, nausea, vomiting, headaches, poor appetite with associated weight loss and low bone density).

Factors affecting vitamin D status include: geographic location (UVB radiation is weaker at higher latitudes), sunscreen use (blocks UVB radiation), skin pigmentation (melanin is a natural sunscreen- the darker your skin, the less efficient the body is at synthesizing vitamin D), obesity (excess body fat reduces our ability to utilize vitamin D) and age (as we age our bodies become less efficient at producing vitamin D).

Since our parathyroid glands regulate vitamin D utilization via blood calcium levels and parathyroid hormone release, a thorough assessment of one’s vitamin D status should really include testing of PTH, calcium and active vitamin D3 levels. Severe calcium deficiency, vitamin D deficiency and chronic kidney failure can all have a profound impact on bone health due to the disruption in calcium homeostasis. Therefore, suppression of PTH levels is extremely important.

Putting this all together:  First and foremost, do not supplement blindly.

If your levels are less than 20 ng/mL, UVB exposure and oral supplementation would be appropriate. If ranging from 20-35 ng/mL, get your PTH level tested and if adequately suppressed (less than 30 pg/mL per Functional Medicine Practitioner Chris Kresser), supplementation is likely unnecessary. If ranging from 35-50 ng/mL, continue frequent monitoring and/or diet and supplementation. And if >50 ng/mL, you may want to consider cutting back on supplementation to avoid toxicity. If supplementing, consider a product containing vitamin K2 and/or cod liver oil and balance nutrient intake via diet appropriately (see recommendations below).

So why not just obtain vitamin D from our diet: Few foods actually contain vitamin D and the foods that do many people tend to limit. However, if trying to avoid supplementation and optimizing your levels, try increasing your intake of sardines, bluefin tuna, mackerel, herring, trout, egg yolks or beef liver. Cod liver oil also contains vitamin A and D though do purchase with caution due to the possibility of rancidity, poor quality products, lack of regulation within the industry and excess amounts of preformed vitamin A (retinoids). Typical recommendations for dosage is one teaspoon.

Regarding vitamin A, both retinoids and carotenoids are essential to health. Preformed vitamin A has specific immune, inflammatory, genetic and reproductive-related benefits and is particularly important in respect to pregnancy, childbirth, infancy, growth, night vision, red blood cell protection and resistance to infectious diseases. The type of vitamin A found in plant foods (carotenoids) also provides us with unique benefits, functioning as a potent antioxidant and anti-inflammatory agent. While carotenoids can be converted to the preformed type of vitamin A (retinoids), many individuals may be poor converters due to inherited genetic tendencies. Factors affected this protective conversion process include genetics, digestive issues, bacterial imbalance or overgrowth within the digestive tract, excessive alcohol intake, exposure to toxic chemicals and improper intake/over supplementation of preformed vitamin A and vitamin D. Plant sources such as sweet potato, carrots, leafy greens (i.e. spinach, kale and swiss chard), winter squash, bok choy, bell peppers, broccoli and parsley are all foods that should be consumed regularly due to their overall high nutrient density. 

How to protect against toxicity: Get sunlight or UVB exposure as your primary form of vitamin D (caution tanning beds if at increased risk of skin cancer). Consume a wide range of nutrient-dense foods including non-starchy and starchy vegetables (i.e. sweet potatoes), fruits (bananas, plantains, avocado), fatty fish (salmon, sardines), grass-fed meats, pasture-raised eggs and grass-fed full fat dairy.

Spotlight on sunlight: Vitamin D is but one benefit that is associated with exposure to both UVB and UVA sunlight. Other important compounds that are produced when are skin is exposed to these types of sunlight includes a natural opiate that causes relaxation and increases pain tolerance, vasodilators which works to reduce blood pressure, inflammation and damage to our DNA, hormones that reduce appetite, increases libido and controls cortisol release by our adrenal glands thereby regulating our immune system and inflammatory processes.