Seasonal fluctuations in serum concentrations of vitamin D metabolites

Brazilian consensus on photoprotection

Brazil is a country of continental dimensions with a large heterogeneity of climates and massive mixing of the population. Almost the entire national territory is located between the Equator and the Tropic of Capricorn, and the Earth axial tilt to the south certainly makes Brazil one of the countries of the world with greater extent of land in proximity to the sun. The Brazilian coastline, where most of its population lives, is more than 8,500 km long. Due to geographic characteristics and cultural trends, Brazilians are among the peoples with the highest annual exposure to the sun. Epidemiological data show a continuing increase in the incidence of non-melanoma and melanoma skin cancers. Photoprotection can be understood as a set of measures aimed at reducing sun exposure and at preventing the development of acute and chronic actinic damage. Due to the peculiarities of Brazilian territory and culture, it would not be advisable to replicate the concepts of photoprotection from other developed countries, places with completely different climates and populations. Thus the Brazilian Society of Dermatology has developed the Brazilian Consensus on Photoprotection, the first official document on photoprotection developed in Brazil for Brazilians, with recommendations on matters involving photoprotection.

Effects of ambient sunlight and photoprotection on vitamin D status

Ultraviolet B radiation exposure is responsible for the majority of natural vitamin D stores in humans. The physiologic role of vitamin D in health and disease is continually expanding, and at the same time the population that is vitamin D deficient is increasing. The environmental characteristics and personal physical traits that contribute to vitamin D3 synthesis from sun exposure are discussed, and the effects of photoprotection on vitamin D status are examined. It is concluded that sunscreen, in the manner used by the general public, does not cause vitamin D insufficiency. Implementing guidelines suggesting sun exposure duration for sufficient vitamin D3 production is limited by the complex interaction of contributory factors, and no recommendation can be made that is both safe and accurate enough for general public usage.

Discrepancy between serum 1,25-dihydroxycholecalciferol measured by radioimmunoassay and cytosol radioreceptor assay

A radioimmunoassay for determination of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) in serum, was compared with the radioreceptor assay using cytosol receptor from rachitic chick intestine in order to clarify whether differences in specificity can explain discrepancies in the clinical application of the two techniques. In the literature, seasonal fluctuations in serum 1,25(OH)2D3 are only observed when using radioimmunoassay. Treatment of anticonvulsant osteomalacia with vitamin D3 results in a marked increase in radioimmunologically measured 1,25(OH)2D3, but no effect on the serum 1,25(OH)2D level, measured by the radioreceptor assay, could be observed. The present study demonstrates that another unknown compound is coeluted on high pressure liquid chromatography with 1,25(OH)2D3, and recognised only by the antiserum. It can be concluded that the present radioimmunoassay cannot replace the cytosol receptor assay or either supplement by measuring the 1,25(OH)2D3 metabolite only.

Familial hypocalciuric hypercalcaemia. II. Intestinal calcium absorption and vitamin D metabolism

We compared intestinal calcium absorption, measured by a single isotope technique, and serum concentrations of vitamin D metabolites in ten patients with familial hypocalciuric hypercalcaemia (FHH) and ten age- and sex-matched healthy controls. Our results showed no significant differences in intestinal calcium absorption or in serum concentrations of vitamin D metabolites. There was a significant correlation between serum concentrations of PTH, measured with one of our assays, and 1,25(OH)2D. We conclude that neither increased intestinal calcium absorption nor altered vitamin D metabolism plays a part in the hypercalcaemia of FHH.

Testosterone treatment and arginine-induced growth hormone stimulation in male delayed puberty: effects on serum calcium, phosphate and vitamin D metabolites

Hormonal changes after arginine-induced growth hormone stimulation and subsequent testosterone treatment were examined in 5 patients classified as having male delayed puberty. All the patients responded well to growth hormone stimulation and a significant negative correlation was found between the delay in height age and the maximal growth hormone response, r = 0.80, P less than 0.05. The testosterone treatment did not alter this pattern. Changes in PTH, 25OHD, 24.25(OH)2D, and 1.25(OH)2D were examined at 24 h after the infusion. The results showed significant reductions in PTH (P less than 0.05) and 24.25 (OH)2D (P less than 0.05) and a possible increase in 1.25(OH)2D, whereas 25OHD remained unchanged. These results may support the conception of growth hormone as a common denominator of growth and bone metabolism.

Serum 25-hydroxyvitamin D levels in Finnish children aged 2 to 17 years

Serum levels of 25-hydroxyvitamin D (25-OHD) in summer and winter were studied in 564 children aged 2-17 years living in the northern, central or southern parts of Finland. The mean levels of 25-OHD were significantly lower in winter (13.3 +/- 10.8 ng/ml) than in summer (27.2 +/- 10.3 ng/ml) in all age groups (p less than 0.001). The mean 25-OHD levels in the northern part of the country did not differ significantly from the others. In both seasons the levels of 25-OHD were lower in the 11-17 year age group than in younger children. In that age group 22.4% of the children had serum levels of 25-OHD below 5 ng/ml (the limit of risk for rickets), compared to 16.8% of children 6-10 years old and 7.5% of children 2-5 years old, but none of the children showed any laboratory evidence of rickets.

Serum vitamin D metabolites in normal subjects after phototherapy

The serum concentrations of the major vitamin D metabolites (25-hydroxyvitamin D(2 + 3) (25-OH-D), 1,25-dihydroxyvitamin D(2 + 3) (1,25-(OH)2-D), and 24,25-dihydroxyvitamin D(2 + 3) (24,25-(OH)2-D) were studied in 22 healthy male volunteers before and after one or two treatments with whole body UVB or PUVA in conventional doses. The effect of UVB was investigated in the autumn and early spring, whereas the effect of PUVA was investigated only in the autumn. The pre-treatment values of two metabolites were significantly reduced in the spring compared to the autumn level (25-OH-D: 14.0 ng/ml versus 22.0 ng/ml, P less than 0.02; and 24,25-(OH)2-D: 1.23 ng/ml versus 2.74 ng/ml, P less than 0.01), whereas the serum concentration of 1,25-(OH)2-D was not significantly reduced in the spring. After UVB, a small, but not significant, rise in all metabolites was observed in the spring, whereas virtually no changes were measured after UVB or PUVA in the autumn. We conclude that UVB and PUVA do not lead to harmful concentrations of vitamin D metabolites in the blood of healthy subjects.

Serum vitamin D metabolites in epileptic patients treated with 2 different anti-convulsants

The serum concentrations of the vitamin D metabolites 25-hydroxyvitamin D (25OHD), 24,25-dihydroxyvitamin D (24,25(OH)2D), and 1,25-dihydroxyvitamin D (1,25(OH)2D) were measured in 18 epileptic patients and 10 controls. The patients were divided according to the anti-convulsant treatment they had been receiving for at least 1 year: 9 patients had received phenytoin and 9 patients carbamazepine, as the sole anti-convulsant therapy. The serum 25OHD was decreased in the patients on phenytoin (P less than 0.01), whereas the other serum vitamin D metabolites were normal. Moreover, serum alkaline phosphatase was increased (P less than 0.001) and serum calcium was decreased (P less than 0.001) in this patient group. In the patient group treated with carbamazepine (a negligible, liver inductor), changes in serum 25OHD and serum alkaline phosphatase were less pronounced (P less than 0.05), but the same degree of hypocalcaemia (P less than 0.001) was present. Our data suggest that liver induction in epileptic patients on anti-convulsant drugs cannot explain the pathophysiology behind anti-convulsant osteomalacia.