Bone metabolism before and after irradiation with ultraviolet light

Abstract

The beneficial effects of ultraviolet light on cutaneous vitamin D synthesis, calcium metabolism, and bone formation are well known. Regarding the increasing fear of side effects from ultraviolet B (UV-B), lamps with less energy in the UV-B range have been developed. Two spectra with differences in the emission of UV-B have therefore been evaluated for their influence on calcium metabolism. A group of 24 healthy male volunteers was subdivided into two treatment groups. Group 1 was exposed to lamps with higher energy of total UV-B but less energy at the wavelengths below 300 nm than the lamps used in group 2. All subjects were irradiated ten times within 12 days. Exposure time was 3 min in the first session and time of exposure was increased by 10% in every following irradiation (suberythematous doses only). Before the first irradiation, 3 days after the last exposure, and after 4 more weeks, the serum parameters of bone metabolism were determined by standard laboratory methods. Significantly increased levels of 25-hydroxyvitamin D3 were found in both groups. There was only a slight increase of 1,25-dihydroxyvitamin D3. Parathyroid hormone decreased significantly in group 2 only. The data would suggest beneficial effects on bone metabolism for both regimens. The observed effects were more pronounced when shorter wavelengths (group 2) were applied, although the total energy of UV-B was lower in these lamps.

UVB radiation and its role in the treatment of postmenopausal women with osteoporosis

“…This lack of effect on 1,25(OH) 2 D confirm the results of one of our previous investigations (Falkenbach et al 1993), and may be attributed to the tight physiological control which prevents intoxication. 1α-Hydroxylation in the kidney is inhibited by 1,25(OH) 2 D (Larkins et al 1974) and stimulated by PTH (Fraser 1980), so that only in states of severe 1,25(OH) 2 D deficiency with concomitant secondary hyperparathyroidism should a significant increase of 1,25(OH) 2 D be expected after UV radiation.…”

“…There was no significant decrease of serum PTH after UV exposure -as has been observed previously in a study of young, healthy male volunteers (Falkenbach et al 1993) -even in the detailed analysis of either the subjects who had relatively high levels of PTH (>40 pg·ml −1 ) before treatment or those who had not received oral vitamin D supplements. In a previous study (Falkenbach et al 1993) the greatest alteration in bone metabolism was observed to occur 4 weeks after the last dose of UV radiation.…”

“…In a previous study (Falkenbach et al 1993) the greatest alteration in bone metabolism was observed to occur 4 weeks after the last dose of UV radiation. It is possible that in the present investigation the interval between cessation of UV treatment and the taking of the second blood sample was too short for measureable effects to be revealed.…”

“…In postmenopausal osteoporosis, which is characterized by increased bone resorption (Nordin et al 1981), lower levels of serum PTH in winter would be favourable with regard to bone mineralization. In a previous study of young healthy volunteers, we observed a significant decrease of serum PTH after serial exposure to UV radiation during the winter (Falkenbach et al 1993). For the assessment of osteoblast function we measured the serum concentration of osteocalcin, which is a specific marker of bone formation (Browne et al 1984) and has been shown to increase after stimulation by 1,25-dihydroxyvitamin D (1,25(OH) 2 D) (Duda et al 1987).…”

Unchanged response to stimulation of pituitary hormone release after serial UV irradiation in men

“…This, however, cannot be the reason as we have previously observed a significant increase of 25 (OH)-vitamin D after a similar protocol of UV treatment (Falkenbach et al 1993).…”