Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease

Abstract

Most humans depend on sun exposure to satisfy their requirements for vitamin D. Solar ultraviolet B photons are absorbed by 7-dehydrocholesterol in the skin, leading to its transformation to previtamin D3, which is rapidly converted to vitamin D3. Season, latitude, time of day, skin pigmentation, aging, sunscreen use, and glass all influence the cutaneous production of vitamin D3. Once formed, vitamin D3 is metabolized in the liver to 25-hydroxyvitamin D3 and then in the kidney to its biologically active form, 1,25-dihydroxyvitamin D3. Vitamin D deficiency is an unrecognized epidemic among both children and adults in the United States. Vitamin D deficiency not only causes rickets among children but also precipitates and exacerbates osteoporosis among adults and causes the painful bone disease osteomalacia. Vitamin D deficiency has been associated with increased risks of deadly cancers, cardiovascular disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes mellitus. Maintaining blood concentrations of 25-hydroxyvitamin D above 80 nmol/L (approximately 30 ng/mL) not only is important for maximizing intestinal calcium absorption but also may be important for providing the extrarenal 1alpha-hydroxylase that is present in most tissues to produce 1,25-dihydroxyvitamin D3. Although chronic excessive exposure to sunlight increases the risk of nonmelanoma skin cancer, the avoidance of all direct sun exposure increases the risk of vitamin D deficiency, which can have serious consequences. Monitoring serum 25-hydroxyvitamin D concentrations yearly should help reveal vitamin D deficiencies. Sensible sun exposure (usually 5-10 min of exposure of the arms and legs or the hands, arms, and face, 2 or 3 times per week) and increased dietary and supplemental vitamin D intakes are reasonable approaches to guarantee vitamin D sufficiency.

1,25‐dihydroxyvitamin D3 promotes IL‐10 production in human B cells

“…In vitro, calcitriol-stimulated dendritic cells can promote the development of Treg cells [10] and calcitriol directly enhances expression of IL-10 by Th cells [11]. Acquired vitamin D deficiency has been correlated to increased prevalence and severity of inflammatory immune-mediated diseases, such as rheumatoid arthritis [2,36], multiple sclerosis [37,38], but also is discussed in context with allergic asthma [4] and atopic dermatitis [5,39]. Furthermore, VDR haplotypes with putatively reduced effector function correlate with increased incidence of multiple sclerosis [40] and allergic asthma [41,42].…”

“…In humans, most calcitriol is produced endogenously, by CYP1a-mediated conversion of nutritionally acquired precursors in the kidneys [2,23]. Extrarenal production of calcitriol has been shown in primary human myeloid cells.…”

“…Epidemiological and experimental data suggest that 1,25-dihydroxyvitamin D 3 (calcitriol)-mediated signaling is involved in the regulation of protective inflammatory processes against harmful pathogens [1] versus anti-inflammatory processes, preventing autoimmunity and allergy [2][3][4][5]. IgE is the key effector molecule of type-I-allergic diseases, such as hay fever or allergic asthma [6].…”

Impact of national fortification of fluid milks and margarines with vitamin D on dietary intake and serum 25-hydroxyvitamin D concentration in 4-year-old children

“…It has, for example been shown that a low intake may be a risk factor for diseases such as type I diabetes (Hyppönen et al, 2001), colorectal cancer (Gorham et al, 2005) and multiple sclerosis (Cantorna et al, 1996). Thus, a higher recommendation for vitamin D intake, 7.5 mg/day, as the conductance of the study has been given in Scandinavian countries (Nordic Nutrition Recommendations, 2004) and a higher cutoff point for serum 25-hydroxyvitamin D, 80 nmol/l has also been suggested (Holick, 2004;Heaney, 2005) to improve the vitamin D status and its health effects in the population. Adopting these new recommendations, two-thirds of children even after fortification of vitamin D in this study evinced poor vitamin D status as estimated by both dietary intake and serum 25-hydroxyvitamin D concentration.…”

Optimal vitamin D levels in Crohn's disease: a review

“…Vitamin D has long been recognised as a major regulator of calcium and phosphorus metabolism and thus has key roles in bone formation and resorption (6)(7)(8) . Low bone mineral density is a common manifestation in Crohn's disease (9,10) and guidelines regarding supplementation are well established (11) .…”