Endocrine Abstracts

Background

There is no universal consensus regarding vitamin sufficiency status with values either above 20 ng/ml, or 30 ng/ml being quoted as denoting ’sufficient’ status. We have endeavoured to assess the effects of summer sunshine exposure on vitamin D status from a single GP practice in central Poland.

Subjects and methods

We measured concentrations of vitamin D, parathyroid hormone (PTH), creatinine and total calcium in 132 subjects (56 males), age 29.36 ± 13.57 years (range 6–50 years), BMI 25.32 ± 6.33 kg/m² in spring and subsequently in autumn (n = 125).

Results

There was an overall increase in vitamin D concentrations from 18.1 ± 7.39 ng/ml to 24.58 ± 7.72 ng/ml, P < 0.001, accompanied by a decrease in PTH from 44.4 ± 17.76 pg/ml to 36.6 ± 14.84 pg/ml, P < 0.001, without significant change in calcium concentrations (P = 0.65). Vitamin D concentrations were lower in spring in males (16.5 ± 6.82 ng/ml vs 19.38 ± 7.62 ng/ml, P = 0.02, for males & females, respectively), but these sex differences became insignificant in autumn (23.8 ± 7.11 ng/ml vs 25.36 ± 8.1 ng/ml, P = 0.24). In spring only 5.3% were vitamin D sufficient for a 30 ng/ml cut-off, with an increase to 23.2% in autumn, P < 0.001. In contrast, where a 20 ng/ml cut-off was employed, then vitamin D sufficiency was found in 34.1% in spring and in 66.4% individuals in autumn, respectively, P < 0.001. Correspondingly, vitamin D deficiency was noted in 62.1% and 29.6%, P < 0.001 (spring vs autumn), for a 20 ng/ml cut-off, but only in 17.4% (spring) and 2.4% (autumn), P < 0.001 for a 12 ng/ml vitamin D cut-off. In multivariate analysis neither BMI, nor age were important determinants of summer vitamin D increase, if at least two week period of holiday leave was taken into account (P < 0.001).

Conclusions

Holiday leave for at least two weeks is the strongest determinant of an increase in vitamin D concentrations. If the majority of healthy individuals fail to reach a 30 ng/ml vitamin D cut-off after summer sunshine exposure, then this raises the question, whether such cut-off is too high, and a 20 ng/ml vitamin D sufficiency cut-off should be universally employed.