Study summary · research use only
The Impact of Minimal Sunlight Exposure on Bone Health: Insights From a Cohort Study in Erythropoietic Protoporphyria
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This longitudinal ambispective single-center cohort study in adult human patients with erythropoietic protoporphyria (EPP) examined risk factors for low bone mineral density (BMD) and associations with cholecalciferol and afamelanotide. Among 139 patients, 82.7% had a Z-score below 0 SD at baseline, with osteopenia in 39.5% and osteoporosis in 15.3%; 34.2% of patients had a total of 50 osteoporosis-related fractures. Aging, persistent vitamin D deficiency, and lower body mass index were associated with increased odds of low BMD. Vitamin D deficiency and no cholecalciferol use at baseline were associated with the highest odds of BMD improvement. Afamelanotide was not associated with a change in BMD.
Abstract
Erythropoietic protoporphyria (EPP) is a rare inherited metabolic disease, causing lifelong painful phototoxic reactions, minimal sunlight exposure, and vitamin D deficiency. Previous studies reported a high osteoporosis prevalence in EPP patients. To identify those at risk for low bone mineral density (BMD) and assess which factors, including treatment with cholecalciferol and afamelanotide, improve BMD in EPP. A longitudinal ambispective single-center cohort study. Data from patient files and two-time questionnaires from adult patients with EPP who underwent at least one dual-energy x-ray absorptiometry (DXA) scan between 2012 and 2023 were used. BMD is low in EPP patients, with 82.7% of the 139 patients having a Z-score below 0 SD at baseline. Low BMD classified as osteopenia was found in 39.5%, and osteoporosis in 15.3%. There were 50 osteoporosis-related fractures in 34.2% of patients. Aging (odds ratio [OR] 1.08; CI, 1.03-1.12), persistent vitamin D deficiency (OR 1.11; 95% CI, 1.00-1.23) and a low body mass index (OR 0.91; 95% CI, 0.82-0.99) increased the odds of low BMD. Patients with a vitamin D deficiency (OR 5.51; 95% CI, 1.69-17.92) and no cholecalciferol at baseline (OR 0.22; 95% CI, 0.04-1.34) had the highest odds of improving their BMD. Afamelanotide did not improve BMD. 25-hydroxyvitamin D (25(OH)D) status plays a crucial role in both preventing low BMD and improving BMD. EPP is a natural model for lack of sunlight exposure and vitamin D deficiency, underlining the importance of lifelong adequate vitamin D status for bone health in the general population.
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