Seasonal variations of U.S. mortality rates: Roles of solar ultraviolet-B doses, vitamin D, gene expression, and infections.
J Steroid Biochem Mol Biol. 2017 Jan 11. pii: S0960-0760(17)30003-1. doi: 10.1016/j.jsbmb.2017.01.003. [Epub ahead of print]
Grant WB1, Bhattoa HP2, Boucher BJ3.
1Sunlight, Nutrition, and Health Research Center, PO Box 641603, San Francisco, CA, 94164-1603 USA. Electronic address: wbgrant@infionline.net.
2Department of Laboratory Medicine, Faculty of Medicine, University of Debrecen, Nagyerdei blvd 98, Debrecen, H-4032, Hungary.
3The Blizard Institute, Barts & The London School of Medicine & Dentistry, Queen Mary University of London, London, UK.
Death rates in the U.S. show a pronounced seasonality. The broad seasonal variation shows about 25% higher death rates in winter than in summer with an additional few percent increase associated with the Christmas and New Year's holidays.
A pronounced increase in death rates also starts in mid-September, shortly after the school year begins.
The causes of death with large contributions to the observed seasonality include diseases of the
- circulatory system; the
- respiratory system; the
- digestive system; and
- endocrine, nutritional, and metabolic diseases.
Researchers have identified several factors showing seasonal variation that could possibly explain the seasonal variations in mortality rate.
These factors include
- seasonal variations in solar ultraviolet-B(UVB) doses and serum 25-hydroxyvitamin D [25(OH)D] concentrations,
- gene expression,
- ambient temperature and humidity,
- UVB effects on environmental pathogen load,
- environmental pollutants and allergens, and
- photoperiod (or length of day).
The factors with the strongest support in this analysis are
- seasonal variations in solar UVB doses and
- 25(OH)D concentrations.
In the U.S., population mean 25(OH)D concentrations range from 21ng/mL in March to 28ng/mL in August. Measures to ensure that all people had 25(OH)D concentrations >36ng/mL year round would probably reduce death rates significantly.
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Vitamin D UK 45 year olds Average vitamin D levels in UK vary with season: 14 ng to 29 ng
Dark gray = 45 year-old MEN, light gray = 45 year-old WOMEN
UV varies a ot more with season at high latitudes
This chart might impliy that the amount of change in seasonal death rate would vary with latitude
Perhaps 35% in Northern Canada, 5% in Tobago, vs 25% in the US