Since it is known that vitamin D is of crucial importance in the regulation of the immune system, as well as that the exposure of the body to the sun's UV rays on the skin produces this vitamin, and the intensity of these rays is greatest around the equator (that is, at low latitudes), a study was conducted on how would examine the association between latitude and the death rate from the disease of COVID-19 for different countries. Eighty-eight countries were selected based on their likelihood of providing reliable data. Using the death rate per million population for each country from the 'Worldometer' website, a correlation analysis was made between death rates and latitude.
A very significant, positive correlation was found between lower mortality rates and geographic proximity to the equator (Pearson: r = 0.40; p<0.0001; two-way t-test). Amount squared r of 0.16 means that a country's latitude accounts for 16 percent of the variation in death rates between different nations. Evidence was presented which indicate a direct correlation between exposure to sunlight and reduced mortality.
This study is the first to show a statistically significant correlation between latitude and mortality from the coronavirus, and is consistent with other research linking latitude, vitamin D deficiency, and mortality from the virus. Limitations in this study are noted.
Further research is needed to confirm the association between latitude and deaths from COVID-19 and to determine the optimal amount of safe sunlight exposure to reduce mortality from the coronavirus in people at high risk of vitamin deficiency.
As the coronavirus spread around the world, mortality observed in over 200 countries was found to be higher in those further from the equator compared to those closer to it (website 'Worldometer'). An obvious example is the comparison of Ireland and Singapore, with data from May 11 of this year, whose population is of similar size (4.9 million compared to 5.3 million), the total number of cases was similar (23,135 compared to 23,822); and the number of cases per million of their population was similar (4.685/million versus 4.072/million). However, the number of deaths in Ireland was 297/million, compared to 4/million in Singapore. Despite a similar number of cases, Ireland had 74 times more deaths than Singapore.
By the second week of May 2020, several medical studies had appeared describing significant correlations between vitamin D deficiency (sun exposure), the death rate from the corona virus, and the suspected pathophysiology of death from the disease. Without adequate levels of this vitamin, the lungs are vulnerable to fatal disruption of the immune system, including but not limited to: cytokine storms, inadequate protection against apoptosis of epithelial cells, and failure to repair these cells.
Since direct sunlight on the skin produces vitamin D in the human body, it is assumed that the population with more regular exposure to the sun's natural UV-rays could have more of this vitamin in the body - unlike those people who are less exposed to the sun, so the latter would be the first consequently had a lower mortality rate from COVID-19. Although exposure to UV rays from sunlight is affected by many factors: such as clouds, weather and air pollution, proximity to the equator also affects exposure to these rays, as their intensity is greater the closer we are to the equator. This study was conducted to examine the correlation between proximity to the equator and the death rate from the corona virus. To test this assumption, a correlation analysis was done that compared latitude and the death rate from COVID-19 per million inhabitants. In order to achieve greater reliability of data on reported deaths, this study attempted to include only countries whose governments have a more favorable "history of transparency". Transparency International ranks a total of 180 countries listed: from most to least transparent, based on multiple criteria of government transparency. Only 90 countries in the top 50% were selected to be included in this study. Latitude data was provided by csgnetwork.com using the capital of each country, with the exceptions of China and Italy, whose vast majority of patients were concentrated at latitudes different from their capitals. The width of the city of Wuhan was used instead of Beijing for China, and for Italy they used Milan instead of Rome.The number of deaths per million inhabitants for each country was taken from the website 'Worldometer' on May 17, 2020. Deaths per million people, as well as geographical widths for each of the 88 countries were entered independently twice on separate occasions and the data compared to ensure accuracy. Pearson's was calculated r correlation on both datasets using Google Sheets "Correlation" and has been compared for accuracy and consistency.
Results and interpretation
Pearson's product-moment correlation on both data sets yielded a correlation coefficient r = 0.40, which gives the coefficient of determination (r squared) = 0.16; that is, 16% of the difference in death rates is attributed to latitude. Such a high correlation for such a crude factor as latitude is surprising, but plausible given other studies showing significant correlations between sunlight exposure and cancer incidence. Lower cancer risks were found in countries with higher levels of sunlight exposure. One study compared the incidence of cancer in sunny countries at lower latitudes with the incidence in less sunny countries at higher latitudes and concluded "that vitamin D production in the skin reduced the risk of several solid cancers (especially stomach, colon, liver and gall bladder, pancreas, lungs, female breast, prostate, bladder and kidney)". Significantly lower rates of prostate cancer were found in men whose birthplace and longest residence was in the southern US states, leading the authors to conclude that "exposure to sunlight reduces the risk of prostate cancer." Deaths from prostate cancer in America were compared in relation to exposure to UV-B ultraviolet light and the results were very significant r = −0.0001 ), which means that men who received more sunlight died less often from prostate cancer. This study found a strong correlation between latitude and death from the corona virus; this connection can be explained by the role of sunlight, which produces vitamin D in the skin; there are other similar studies that link the lack of this vitamin with deaths from the disease COVID-19. Although we are not directly dealing with this vitamin here, its production in the human body due to exposure to UV rays from sunlight, as well as the known increase in intensity of these rays closer to the equator, suggests the possibility that populations closer to the equator have higher levels of endogenous vitamin D (thereby reducing the likelihood fatal dysfunction of the immune system in the presence of the corona virus), compared to the population living further from the equator.
The importance of sunlight in the fight against the disease COVID-19 is well seen by comparing the statistics that include Milan and Naples in Italy. It is known that the sun's UV rays reach the ground little or not at all during the winter months in countries whose latitude is above 40°. Milan is located at a latitude well above 40° (45.46° N), and the corona virus epidemic spread rapidly during February 2020. As of May 21, 2020, the death rate was 15,729 per million. Naples is located at 40.85 N, which is 318 miles south of Milan's latitude; however, Naples has 59% sunny days per year compared to Milan's 43% sunny days. On May 21, 2020, Naples' death rate was 403 per million, compared to Milan's 15,729 per million, which is only 3% of Milan's death rate. In this comparison, the fact that Naples is closer to the equator is less significant than the difference in their annual exposure to sunlight. Compared to Milan, Naples enjoys 58 more sunny days during the year, which for its population is almost two more sunny months each year. This comparison supports the hypothesis that the basic mechanism behind the association between latitude and mortality is precisely the consequence of a significant difference in exposure to ultraviolet rays and consequently different levels of endogenous vitamin D in the respective populations.
Limited exposure to sunlight for people in institutions (such as prisons, some health care facilities, and nursing homes) is thought to be the reason 75% of this population is vitamin D deficient and suffers from a disproportionately high mortality rate from the coronavirus. Lower levels of this vitamin are also associated with advanced age, diabetes and hypertension - these are the same 3 risk factors associated with deaths from the corona virus and are generally common in the population of nursing homes. Even if nursing home patients get an adequate amount of vitamin D through their diet, it may not be enough, as some studies show that dietary vitamin D is less effective than that produced in the body through exposure to sunlight.
Discussion and conclusions
This study is the first to document a statistically significant correlation between latitude and mortality from the coronavirus. Extremely significant probability (p<0.0001) that countries closer to the equator have lower mortality rates from COVID-19 than countries further away, supports a plausible relationship between latitude, sunlight exposure, vitamin D and mortality from coronavirus. Most likely, this connection can be explained by the mechanism of this vitamin, which is induced by sunlight. Further efforts are needed to see whether endogenous vitamin D is a protective factor against COVID-19 and, if so, what is the optimal amount of safe sunlight exposure to produce a protective effect.
It is important to note that exposure to sunlight does not bring equal benefits to all members of the population. The efficiency with which UV rays on the skin produce endogenous vitamin D changes according to the age, skin color and gender of the person. The body's efficiency in producing this vitamin from sunlight declines with age: elderly women in Ecuador (where sunlight is abundant) have been shown to suffer from vitamin deficiency. Darker skin color reduces vitamin D production, and this may be one of the reasons African Americans are twice as likely to be deficient in vitamin D compared to the general population (82.1% vs. 41.6%), as well as the disproportionately high death rate from COVID-19 in the dark-skinned population. In addition to skin color and age, the local customs of the inhabitants can also affect the results of UV exposure: vitamin D deficiency has been found in girls and women in the Middle East, despite the abundance of sunlight.
An important limitation of this study is the unknown elapsed time between the identification of the first cases in a country and the reported mortality rates. All other factors being equal, the death rate in a country where cases started appearing recently will appear to be lower than in countries that have been fighting the virus longer. Such variability could increase or decrease the numbers used in a correlation study, depending on the latitude of the country. This does not seem to have changed the striking difference between death rates in Ireland and Singapore, which we mentioned in the introduction. On 11 May 2020, the 'Worldometer' recorded 297 deaths per million in Ireland, compared to just 4 deaths per million in Singapore. On 20 June 2020, 347 deaths/million were reported in Ireland and still only 4 deaths/million in Singapore. Despite the fact that over the past 5 weeks, the number of people suffering from the corona virus in Singapore has increased by 75% (from 4.072/million to 7.152/million), and in Ireland this number has increased by 10% (from 4.685/million to 5.141/million), the rate the death rate in Singapore remained stable at 4 deaths/million. Although Ireland appears to have slowed its case rate compared to Singapore, it now has a death rate 86 times that of Singapore. This comparison is not only consistent with the positive correlation between equatorial proximity and low death rates, it also shows that the difference in reported death rates for this pair of countries is not the result of different time durations from diagnosis to death.
The above comparison may be an anomaly and the fact remains that the unknown time period from the first identified cases to the reported deaths in our 88 countries represents a possible confound in these results. Statistical probability tests cannot eliminate this difficulty, but they can reduce the probability of falsely inferring a significant correlation. What is the value of "p” more extreme, the less likely it is to falsely find a correlation that does not exist (ie, to make a “type 1 error” in a statistical hypothesis test).
The results of this study support those of other such studies, which point to an urgent need to compensate for vitamin D deficiency in order to reduce deaths from COVID-19. Further research is needed: how much safe sunlight exposure is needed, as well as consideration of oral vitamin D supplementation, as these supplements – although only partially effective – are cheap, safe to use and relatively easily available. The goal that needs to be focused on as soon as possible is: how to strengthen the immune system (while scientists continue the search for medical treatments and a vaccine) - this would be an "internal" but belated addition to the "external" (social distance, masks, disinfectants) strategies fighting for health against the corona virus.
More about the importance of proper sunbathing: https://detoksikacija-organizma.com/7-najvecih-dobrobiti-sunca-za-zdravlje/
