Give the role of both of these nutrients in cellular energy production, this finding is not at all surprising. Also, vitamin D is a known inhibitor of the enzyme tryptophan hydroxylase (TPH), which synthesizes serotonin (5-HT). Thus, low vitamin D levels mean higher activity of TPH and thus more serotonin production. Elevated tryptophan and serotonin have already been linked to premature graying and anti-serotonin drugs of the ergot class (e.g. bromocriptine) have been shown to reverse hair graying in humans.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3746220/
“…Researchers have also flagged low vitamin D and calcium as common in people with premature graying. A 2013 case-control study our of a semi-urban Indian population found deficiencies in serum calcium and vitamin D3 among the group with premature graying.”
