Vitamin D: A millenium perspective

Abstract

Vitamin D is one of the oldest hormones that have been made in the earliest life forms for over 750 million years. Phytoplankton, zooplankton, and most plants and animals that are exposed to sunlight have the capacity to make vitamin D. Vitamin D is critically important for the development, growth, and maintenance of a healthy skeleton from birth until death. The major function of vitamin D is to maintain calcium homeostasis. It accomplishes this by increasing the efficiency of the intestine to absorb dietary calcium. When there is inadequate calcium in the diet to satisfy the body's calcium requirement, vitamin D communicates to the osteoblasts that signal osteoclast precursors to mature and dissolve the calcium stored in the bone. Vitamin D is metabolized in the liver and then in the kidney to 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. 1,25(OH)(2)D receptors (VDR) are present not only in the intestine and bone, but in a wide variety of other tissues, including the brain, heart, stomach, pancreas, activated T and B lymphocytes, skin, gonads, etc. 1,25(OH)(2)D is one of the most potent substances to inhibit proliferation of both normal and hyperproliferative cells and induce them to mature. It is also recognized that a wide variety of tissues, including colon, prostate, breast, and skin have the enzymatic machinery to produce 1,25(OH)(2)D. 1,25(OH)(2)D and its analogs have been developed for treating the hyperproliferative disease psoriasis. Vitamin D deficiency is a major unrecognized health problem. Not only does it cause rickets in children, osteomalacia and osteoporosis in adults, but may have long lasting effects. Chronic vitamin D deficiency may have serious adverse consequences, including increased risk of hypertension, multiple sclerosis, cancers of the colon, prostate, breast, and ovary, and type 1 diabetes. There needs to be a better appreciation of the importance of vitamin D for overall health and well being.

Reflected solar radiation from horizontal, vertical and inclined surfaces: Ultraviolet and visible spectral and broadband behaviour due to solar zenith angle, orientation and surface type

“…Exposure to biologically effective ultraviolet (UV) radiation can be beneficial to human health in the form of initiating pre-vitamin D 3 formation [1] and detrimental; such as erythema, skin cancer, ocular damage and more [2]. UV exposure is specific to the formation of the above health effects and much research has been conducted to measure and model UV exposure.…”

Vitamin D deficiency in minority populations

“…The majority of vitamin D is estimated to derive from sunshine for most people (26) , with the liver converting cholecalciferol into 25(OH)D 3 , the form of vitamin D typically measured in blood serum. 25(OH)D 3 has a reported half-life of 15 d (27) , and therefore decreases from summer (when solar radiation is highest) to winter (28) .…”

“…A growing literature (1)(2)(3) suggests that vitamin D may be associated with reduced mortality (overall (4) and hospital-associated (5) ), incidence of cancer (6)(7)(8)(9)(10)(11)(12)(13) , CVD (14,15) , diabetes (16) , fractures (17,18) and ageing-related functional limitations (19) , although some studies find an unclear relationship (20,21) or a harmful association with disease (22) . Randomized controlled trials are underway to examine the potential role of vitamin D in the prevention of multiple diseases, including cancer, CVD and diabetes (20,23) .There are known racial and seasonal variations in vitamin D. Black individuals synthesize less vitamin D per unit of sun exposure than white individuals, because darker complexion acts as a natural sunscreen (24,25) .The majority of vitamin D is estimated to derive from sunshine for most people (26) , with the liver converting cholecalciferol into 25(OH)D 3 , the form of vitamin D typically measured in blood serum. 25(OH)D 3 has a reported half-life of 15 d (27) , and therefore decreases from summer (when solar radiation is highest) to winter (28) .…”

Influence of reflected UV irradiance on occupational exposure from combinations of reflective wall surfaces

“…[1][2][3][4] Conversely it can be detrimental in excessive quantities through an increased induction of erythema (sunburn), non-melanoma and melanoma skin cancer, ocular damage, DNA damage 5 and is linked to immunosuppression and photo aging. 6 Populations of UV sensitive people are generally at risk from damage due to UV radiation when living in areas of high ambient UV radiation, however that risk is increased in members of the population who occupationally spend working hours exposed to solar UV radiation [7][8][9] depending on skin type and individual factors.…”