Cath Lab Digest

     During the past two decades, research on vitamin D has increased exponentially. Healthcare practitioners have learned vitamin D plays a much more important role in disease prevention and well-being than was ever suspected. This new information comes in stark contrast to behavioral trends. In the 1980s, sun exposure was demonized and we became an indoor society. Because sun exposure is one of the best ways to obtain vitamin D, the lack of sunshine plus zealous use of sunscreen has contributed to a vitamin D-deficient society.

     Vitamin D deficiency is now regarded as a global health problem, but despite an abundance of media attention, many physicians and their patients remain unaware of the possible ill effects of vitamin D deficiency. Current estimates are that 50% to 78% of the population has inadequate stores of vitamin D and the incidence is even greater in high-risk groups, such as African Americans and homebound elderly.¹

Forms of Vitamin D

     Vitamin D actually refers to a pair of inactive precursors to a critical hormone. Cholecalciferol, more commonly known as D3, is produced in the skin after exposure to ultraviolet B light (UVB) or from foods we consume. Ergocalciferol, also known as D2, is produced in plants and enters the body through diet. Once D2 and D3 are present in circulation, they are bound to vitamin D-binding proteins (VDBP) and hydroxylated in the liver to form 25-hydroxyvitamin D (25[OH]D) or calcidiol. A further conversion in the kidney changes the calcidiol to 1,25-dihydroxyvitamin D (1,25[OH]2D) or calcitriol.

     Calcidiol is the main circulating and storage form of vitamin D in the blood, with a half-life of approximately 3 weeks. This is the preferred form to evaluate vitamin D status in patients. Because the production of calcitriol is tightly regulated with a half-life of only 4 to 6 hours, its measurement is usually only of interest in renal disease or primary hyperparathyroidism.²

Vitamin D Deficiency

     Numerous risk factors may predispose an individual to vitamin D deficiency³:

     • Limited sun exposure, including constant use of sunscreens when outdoors. Sunscreens with a sun protection factor (SPF) of 15 block 99% of the UVB rays that make vitamin D in our skin;
     • Cultural dress, such as hijabs or burkas worn by Muslim women⁴;
     • Limited intake of foods that provide vitamin D, such as fortified milk, fortified cereal, and fatty fish. Table 1 lists the vitamin D content of the best food choices and select supplements;
     • Living 40º north of the equator. The farther a person lives from the equator, the less his/her exposure to UVB rays and the less vitamin D produced by the body;
     • Limited use of vitamin D supplements. Typical multivitamins do not provide an adequate amount of vitamin D for optimum health if other sources are not present;
     • Dark complexions. Persons with darker complexions (eg, individuals from Africa, East India, and the Caribbean) may require up to six times the amount of sun exposure to form the same amount of vitamin D from the sun as light-skinned or Caucasian people;
     • Aged skin. In general, people >60 years of age have a 25% reduction in cutaneous formation of vitamin D. Senior citizens who are homebound or in long-term care facilities are at very high risk for vitamin D deficiency;
     • Obesity. Because vitamin D is fat-soluble, it appears to be sequestered in adipose stores and not released easily into the blood for use by the body;
     • Malabsorption disorders, including Crohn’s disease, celiac disease, and cystic fibrosis.