A geographical approach to the development of hypotheses relating to Covid-19 death rates

Covid-19 deaths per million vary greatly between continents, with countries in South America having higher death rates even than Europe and North America, while Asia, Africa and Oceania have death rates which are only a fifth of those in South America.  By analysing national level data on body weight, diet and latitude, we hypothesise and demonstrate that difference in the percentage of people with overweight (BMI > 25) may be the major factor that explains these differences in Covid-19 death rates. Meanwhile, within the group of countries where adult overweight is prevalent (i.e., where more than 50% of the population has BMI > 25), we hypothesise and demonstrate that latitude plays a role, with relatively lower death rates occurring in countries at lower latitudes. We further suggest that these relationships may be explained by two possible medical hypotheses relating to solar radiation: (1) In overweight people there is less penetration to important organs of near-infrared radiation (NIR) which stimulates production of subcellular melatonin, a strong anti-oxidizing factor and (2) In overweight people, fatty tissue holds much of the body´s 25(OH)D3 leaving less circulating in the blood stream.  Several pathways have been proposed by other researchers to explain the link between Vitamin D deficiency and severity of Covid-19, but the possible link of Covid-19 outcome with NIR has not been explored. Latitude, of course, determines the amount of incoming NIR and as well as UV-B, which is the main stimulant for the body´s production of Vitamin D. It may well be that these two physiological processes operate simultaneously.