In the dark of night

Yesterday's sunset over New York

Daylight Saving Time has finished for another year. Our clocks have gone back an hour. The difference is quite a shock. At 3:00pm this afternoon I found myself turning on the lights at Swiss Cottage in an attempt to alleviate the gloom. By 5:00pm it was dark outside. Winter is clearly on its way.

I saw some interesting statistics on the duration of daylight at different times of the year yesterday. USA Today published a chart which showed Daylight in Minneapolis lasting 10 hours and 8 minutes on November 2, compared with 15 hours and 33 minutes on July 1. The difference is even more extreme in London. Summer's daylight hours extend up to 17 hours, falling to less then 8 hours in winter (shown below).

I read this week that much of the UK and other Northern Europe nations suffer Vitamin D deficiency thanks to winter darkness. Our skin requires UVB rays to make Vitamin D. Most fair-skinned people require at least 15 minutes of sunlight at midday to maintain good health. However, at higher latitudes UVB rays struggle to penetrate the atomsphere in sufficient quantities for much of the year. Food supplements are the only alternative vitamin source. Vitamin D deficiency is one health risk I never anticipated when relocating to London.