From The Telegraph:
‘There’s a certain slant of light, / On winter afternoons” wrote Emily Dickinson, “That oppresses, like the Heft / Of cathedral tunes.” And although humans have developed nature-defying central heating and electric light bulbs since the American poet wrote those lines, many members of our species are still prone to the winter blues, or Seasonal Affective Disorder (SAD). As the weather gets colder and daylight hours dwindle, SAD sufferers feel their energy levels slumping. They can become depressed, lethargic and crave sweet or starchy foods. For despite our cocooning technology we are still, like all life on earth, subjects of the seasons.
In Rhythms of Life (2004), their first book on the fascinating chronobiology that ticks away inside every living cell, Russell Foster (professor of circadian neuroscience at Oxford) and Leon Kreitzman (broadcaster and author of The 24 Hour Society) explained the circadian rhythms generated by the Earth’s 24-hour revolution on its axis. They took us through the science behind flowers opening their petals in the day and folding them up at night, just as we wake and sleep. They advised that the best time of day for giving an impressively firm handshake is around 6pm and the best time for giving birth is between 4am and 6am. Now they’re taking in the bigger picture, pointing out that just as all creatures have an internal, 24-hour clock, so we also have an internal calendar governed by Earth’s 365-day rotation around the sun.