{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,11,3]],"date-time":"2026-11-03T17:15:46Z","timestamp":1793726146578,"version":"4.6.1"},"reference-count":47,"publisher":"Wiley","issue":"3","license":[{"start":{"date-parts":[[2025,5,18]],"date-time":"2025-05-18T00:00:00Z","timestamp":1747526400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2025,5,18]],"date-time":"2025-05-18T00:00:00Z","timestamp":1747526400000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/doi.wiley.com\/10.1002\/tdm_license_1.1"}],"funder":[{"DOI":"10.13039\/501100003554","name":"Lundbeck Foundation","doi-asserted-by":"publisher","award":["R170\u20102014\u2010855"],"award-info":[{"award-number":["R170\u20102014\u2010855"]}],"id":[{"id":"10.13039\/501100003554","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100000724","name":"Health Foundation","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100000724","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Andrology"],"published-print":{"date-parts":[[2026,3]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Vitamin D is metabolised throughout the male reproductive system, suggesting a direct regulatory role of vitamin D in male reproduction.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Objectives<\/jats:title>\n                    <jats:p>To investigate the association between plasma vitamin D levels at sperm ejaculation and during spermatogenesis and biomarkers of male fecundity in young men.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Materials and methods<\/jats:title>\n                    <jats:p>\n                      From the Fetal Programming of Semen Quality cohort, Denmark, 2017\u20132019, 1047 young men provided a semen and a blood sample, and self\u2010measured their testes volume at a clinical visit. Plasma levels of vitamin D (25(OH)D\n                      <jats:sub>3<\/jats:sub>\n                      ) and reproductive hormones were measured in the blood sample. Relative percentage differences in semen characteristics, testes volume and reproductive hormone levels were analysed according to measured vitamin D levels (categorised, continuous and as restricted cubic splines) at sperm ejaculation. Additionally, we used the seasonal variation in endogenous vitamin D synthesis to estimate individual vitamin D levels 3 months prior to sperm ejaculation (at initiation of spermatogenesis) in addition to 2 and 1 month before. This was analysed following the same strategy.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Compared to measured vitamin D levels &gt;75\u00a0nmol\/L, levels &lt;25\u00a0nmol\/L at sperm ejaculation were associated with lower total sperm count (\u201215% [95% confidence interval: \u201233%; 8%]), and a higher proportion of non\u2010progressive and immotile spermatozoa (11% [95% confidence interval: 0%; 24%]). Lower measured vitamin D levels were also associated with higher oestradiol, lower sex hormone\u2010binding globulin and lower follicle\u2010stimulating hormone, in dose\u2010dependent manners. Vitamin D levels estimated before and during spermatogenesis yielded similar associations as vitamin D levels measured at sperm ejaculation.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Discussion<\/jats:title>\n                    <jats:p>By using the seasonal variation in endogen vitamin D synthesis, we were able to estimate individual vitamin D levels during spermatogenesis.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>Lower vitamin D levels before and during spermatogenesis and at sperm ejaculation were associated with lower total sperm count and sperm motility and an altered reproductive hormone profile.<\/jats:p>\n                  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