Vitamin-D is a fat-soluble vitamin that plays a remarkably vital role in human health and immunity. Most notably, vitamin-D increases absorption of calcium, phosphorus, and magnesium in the intestines, thereby playing a critical role in both our physical and mental wellbeing.
Calcium is the most plentiful mineral in the body, and is essential for building strong bones and teeth, but it also helps our blood clot, it allows for our muscles to contract and relax, and keeps our heart beating. Calcium works alongside phosphorus in the formation of bones and teeth, but phosphorus further aids in the body’s production of protein for growth, maintenance, and the repair of cells and tissues. Without vitamin-D, only 10-15% of dietary calcium, and roughly 60% of phosphorus are absorbed. Magnesium is an essential mineral, found mostly in bone, but also found in muscles, soft tissues, and our blood. It is responsible for hundreds of biochemical reactions, which maintain our overall body and brain health. Magnesium helps convert food into energy, helps create and repair DNA and RNA, and helps regulate neurotransmitters, which are responsible for transmitting messages throughout our brain and nervous system.
Calcium, phosphorus, and magnesium are three of the most abundant minerals in the human body, and insufficient vitamin-D ultimately decreases intestinal absorption of these three critical minerals. However, research indicates a deficiency in vitamin-D exceeds far beyond the established effects on bone and calcium homeostasis, as vitamin-D receptors are not solely expressed in skeletal and intestinal tissue. They are additionally present in bone marrow, the brain, the colon, the breast, malignant cells, and immune cells (specifically B cells, T cells, and antigen-presenting cells). Without an adequate amount of vitamin-D, we are putting ourselves at extreme risk of a variety of diseases ranging from obesity, diabetes, hypertension, depression, chronic fatigue syndrome, osteoporosis, and neurodegenerative diseases including Alzheimer’s. However, and perhaps most importantly, a deficiency in vitamin-D also increases our susceptibility to both autoimmune diseases and infection. And we've unknowingly been treating infections with vitamin-D for centuries.
In the 19th century, sanatoriums were created as a means of treating tuberculosis, which is a bacterial disease that mainly affects the lungs. Popular treatments included outdoor walks, physical exercise, and a balanced diet. However, cod liver oil and sunlight (both exceptional sources of vitamin-D) were considered the most effective means of curing the disease. Sunlight, in particular, was thought to “directly kill” tuberculosis when in actuality, patients were merely reaping the benefits of vitamin-D.
Vitamin-D is often referred to as the “sunshine vitamin” because when sunlight hits our skin, a chemical reaction occurs where the body produces cholecalciferol (vitamin-D3), the liver converts it into calcidiol, and lastly, the kidneys convert it into calcitriol. Generally, we absorb 50-90% of the recommended amount of vitamin-D from direct sunlight with the remaining 10% coming from food and supplementation. However, absorbing our daily dose of vitamin-D through the skin would require 15-20min where 40% of the skin surface is exposed to the sun. And this allotment of time increases 3-5x for individuals with darker skin tones. Unsurprisingly, nearly 50% of the world’s population is vitamin-D deficient due to limited sun exposure, with nearly 90% below the required amount for immunity support (>1000IUs). These mindboggling percentages confirm the necessity for vitamin-D supplementation.
Popular foods that are high in vitamin-D include fatty fishes like salmon and sardines, but cod liver oil, canned tuna, egg yolks, mushrooms, and fortified dairy products are also an excellent source. However, many find vitamin-D3 supplements are the fastest and easiest way to ensure we consume our daily allotment of vitamin-D, which is critical for our bone health, our immune system, and our mental wellbeing.