The light on the sunshine vitamin—vitamin D—is shining bright lately and not just in areas of bone health, such as osteopenia, osteoporosis, osteomalacia and hip fractures. In fact, it is also said that vitamin D deficiency may precipitate or exacerbate autoimmune and cardiovascular conditions. But before going into the structure/function applications of vitamin D, it is first important to understand the history and background of this important nutrient.
There are two forms of vitamin D: D2 and D3. Vitamin D2 (ergocalciferol) is found in yeast that has been exposed to ultraviolet B (UV-B) light, while vitamin D3 (cholecalciferol) is a fat-soluble vitamin sourced from the sun or from fish oil or lanolin. Vitamin D3 requires conversion in the liver and kidneys to form the physiologically active hormone form of vitamin D.
Vitamin D is different from all of the other vitamins in human nutrition because it is the only vitamin that is conditional. Humans who are not exposed to sufficient sunlight due to reason of geography, shelter, clothing or atmospheric pollution/sunscreen, which may block UV-B, may require dietary intake of vitamin D. It has been known that even sufficient body stores of vitamin D from summer skin exposure may be inadequate by the end of the winter. Under these conditions, vitamin D is an essential nutrient.
Currently, the Institute of Medicine (IOM) states that the Recommended Dietary Allowances (RDAs) for vitamin D persons aged 0 to 70 should be 600 IU/daily, while persons aged >70 and older should aim for 800 IU. Additionally, the upper limit for daily vitamin D consumption was set to 4,000 IU/daily. This may seem low to many people; however, it is important to note that the IOM is referring to healthy people in the general population who do not have a vitamin D deficiency. If you are healthy and you have a “good” vitamin D status, then as you age (i.e., 70+), you only need to get 600–800 IU of vitamin D daily from your diet and/or sunshine. However, if a deficiency (i.e., <30 ng/mL) is present, then it is important to correct the deficiency with diet and higher potency supplements with the care, and supervision of a physician or healthcare practitioner to improve health.
Structure/Function Application of Vitamin D3
Building strong bones and teeth require the effort of more than just calcium. In fact, vitamin D helps facilitate calcium absorption in the body. Vitamin D also works in concert with a number of other vitamins, minerals and hormones to harden the bones.
Bone consists of calcium and magnesium combined with other ions and minerals to form calcium hydroxyapatite, which provides structural integrity. Bone constantly remodels itself, which is facilitated by the parathyroid hormone and vitamin D via cells that breakdown and reabsorb bone called osteoclasts and cells that, in turn, form and develop bone called osteoblasts. The active hormonal form of vitamin D functions in a similar way as the parathyroid hormone in that it mobilizes calcium stores from bone if dietary calcium intake is too low.
Vitamin D deficiency causes abnormal bone formation. In children, this is known as rickets, a bone disease in which bone mineralization is compromised, resulting in soft bones and skeletal deformities. Vitamin D deficiency can result in osteopenia, osteomalacia or osteoporosis in adults. Osteopenia is low bone mass, which is a risk factor for osteoporosis. Osteomalacia is excess tissue accumulation in unmineralized bone matrix characterized by muscular weakness and softening of the bones, which results in the lack of calcium and/or phosphate being incorporated into the protein bone matrix. Osteomalacia is caused by poor diet, lack of vitamin D and/or lack of exposure to sunlight and has been associated with certain drugs used in the elderly. Osteoporosis is a disease caused by a reduction in the quantity of normally mineralized bone—sometimes due to vitamin D deficiency—and is characterized by fragile bones, which significantly increases the risk of bone fractures.
In addition, to the importance of vitamin D on bone health, researchers from the University of Warwick in the UK performed the first-ever systematic review and meta-analysis looking at the association between blood levels of vitamin D and cardiovascular disease (CVD). Twenty-eight studies giving data on 99,745 participants across a variety of ethnic groups including men and women were included in this meta-analysis, published in the journal Maturitas. Although the potential mechanism of action on how vitamin D works to support cardiovascular health is not fully understood, one theory is that by helping increase calcium absorption into the bone, vitamin D reduces the amount of calcium in the blood. Excess calcium in the blood can cause calcification in the walls of blood vessels resulting in hardening of the arteries (which can also impact blood pressure).
Greenspan, S.L., Resnick, N.M., & Parker, R.A. (2005). Vitamin D supplementation in older women. Journals of Gerontology, 60, 754–759.
Parker, J., Hashmi, O., Dutton, D., Mavrodaris, A., Stranges, S., Kandala, N.B., … Franco, O. H. (2010). Levels of vitamin D and cardiometabolic disorders: Systematic review and meta-analysis. Maturitas, 65, 225–236.
Published in WholeFoods Magazine, February 2013