I am going to reiterate a thought, perhaps a hypothesis. But what if the actual main driver for the benefits of vitamin D is not found purely in the hormone itself but from the light from which it was produced?
We know that sunlight has positive effects on the mitochondria. It has also been shown that sunlight can change the microbiome in positive ways.
Skin exposure to sunlight: a factor modulating the human gut microbiome composition
Background: The gut microbiome has been increasingly acknowledged as playing a pivotal role in human health. Therefore, a number of studies have focused on variables that impact its microbial structure and consequent functionality. A wide range of factors, such as diet, age, sex, life stage, behavior, ethnicity, and diseases have been considered, and strong links were set out. However, some aspects regarding the microbiome determinants are still under-explored. Discussion: Recently, Bosman et al. presented evidence that skin exposure to narrowband UVB light modulated the gut microbiome of a specific human cohort. This cohort presented an increase of biodiversity, Firmicutes and Proteobacteria, and a decrease of Bacteroidetes. Based on these findings, we revisited our data on a hunter-gatherer gut microbiome (Yanomami) and identified similarities in the gut microbiome of these two cohorts. Both presented a high abundance of Proteobacteria, which had been observed as a unique feature in the Yanomami gut microbiome, and based on Bosman et al study, could be associated with their natural sunlight exposure. Conclusion: In this commentary, we would like to point out that the human lifestyle concerning sunlight exposure should be considered as one force modulating the gut microbiome, highlighting, as proposed by Bosman et al, a novel skin-gut axis which is associated with health and disease.
Perhaps we are looking at this backwards. What if Vitamin D is actually a signature biomarker for getting an adequate level of exposure to sunlight? If we do not have enough light exposure we do not get enough Vitamin D.
Perhaps older people go further south for the winters because they have reached a point where they cannot produce adequate amounts of Vitamin D in the skin, so they move closer to the equator where there is more light year round? Endless summer if you will.
Author
J.R.K