Increased 25(OH)D3 level in redheaded people: Could redheadedness be an adaptation to temperate climate?

Abstract

On average, less than 2% of all Europeans (but 6-13% of population of Ireland, Wales and Scotland) express the redheaded phenotype. [1,2] Mutations in the gene for receptor protein MCIR, the most important regulator of melanogenesis, [3] which is responsible for low levels of eumelanin in the affected subjects, probably spread in human populations after the arrival of modern Homo sapiens to Europe. Nevertheless, the most common allele, Val92Met, seems to have introgressed into our gene pool from Homo neanderthalensis. [4] In redheaded subjects, the eumelanin (black pigment) is, for the most part, substituted with a related pigment pheomelanin (yellow-red pigment) in melanin-containing granules in the skin, hair and iris.

Effects of 105 biological, socioeconomic, behavioural, and environmental factors on the risk of SARS-CoV-2 infection and a severe course of Covid-19: A prospective longitudinal study

“…Our data showed that dark-haired women but not men had a lower risk of SARS-CoV-2 infection and a less severe course of Covid-19. This higher resistance of dark-haired subjects is probably the result of generally better health of dark-haired individuals in the Czech population 13,15 . It is thus telling that dark-haired subjects – and even more so subjects with darker skin tone – had also a less severe course of Covid-19 (though it was significant only in women) and reported better physical health in the second questionnaire.…”

“…It has been generally expected that vitamin D ought to protect against Covid-19 12 and it is known that redhaired individuals can synthesise more vitamin D in conditions of lower intensity of UV radiation, that is, in the higher latitudes of temperate zones 13 . We have therefore expected that the intensity of red colour of hair would negatively correlate with the risk of infection or severity of Covid-19.…”

Redheaded women are more sexually active than other women, but it is probably due to their suitors

“…In the project, redheadedness was determined using several methods: participants' self-report in the questionnaire, experimenters' observer report during the laboratory investigation, and two methods of measuring hair pigmentation with a spectrophotometer. A previously published study on the effects of redheadedness on vitamin D concentration, which was performed on the same data, showed that all the above-mentioned indicators of redheadedness correlated very strongly with each other and provided almost identical results (Flegr et al, 2020b). In the present study, we have therefore decided to employ only selfreported redheadedness because this will provide better comparability with various past (Frost et al, 2017;Flegr and Sýkorová, 2019) and future studies about the effects of redheadedness.…”

Latent toxoplasmosis and vitamin D concentration in humans: three observational studies

“…The main sources of infection are food or water contaminated by oocysts from feline faeces and the consumption of raw or undercooked food containing tissue cysts of the parasite (Tenter et al 2000). Recently, new routes of transmission of T. gondii in humans, namely sexual intercourse (Flegr et al 2014a) and oral sex (Kaňková et al 2020), have been proposed. Indeed, Hlaváčová et al (2020) showed that an infected sexual partner could be a new risk factor for women.…”

“…Recently, new routes of transmission of T. gondii in humans, namely sexual intercourse (Flegr et al 2014a) and oral sex (Kaňková et al 2020), have been proposed. Indeed, Hlaváčová et al (2020) showed that an infected sexual partner could be a new risk factor for women.…”