The differential exposure to UVB, that is, sunlight, was the first thing I thought of reading this article. It is especially likely among people born in the in

The differential exposure to UVB, that is, sunlight, was the first thing I thought of reading this article. It is especially likely among people born in the industrial-era 19th century, at a time before the nature of the link between health and sunlight was clearly identified. Around a hundred years ago, the role of UV in preventing rickets was confirmed. By the 1930's, vitamin D supplementation of foods became widespread, and the most obvious manifestations of deficiency (e.g., rickets) essentially disappeared. Studied intensively since the 1930's numerous effects of D (or lack of it) have been reported, and recently interest has exploded. Increasingly evidence implicates low vitamin D levels in a wide range of conditions, such as autoimmune disorders, cancer, and metabolic disease, that are likely contributors to reduction of life expectancy. Seasonality of vitamin D level is well known. In northern latitudes (>=45th parallel) the nadir occurs around March-April, and the peak is measured on average in September-October. The timing of these fluctuations appears quite congruent with the article's assertions about life expectancy, so it's reasonable to think there is a connection. For anyone interested in vitamin D, I highly recommend this excellent review: http://www.tandfonline.com/doi/full/10.4161/derm.24494 http://www.tandfonline.com/doi/full/10.4161/derm.24494