I learned many interesting things at the New York Academy of Sciences conference on "Circadian Disruption and Cancer."
I came home, removed a blue nightlight from my bathroom, and installed light-blocking shades on the windows in my bedroom. I also began to shut the door to my bedroom while sleeping. I am determined to never expose myself to light during sleeping hours, especially during the key melatonin-producing hours of 3 and 5 am. The results have been remarkable. My sleep has been better, I haven't had to get up at all during the night, and I awake more refreshed. There may be other, long-term benefits as well. In the next few newsletters I want to talk about how sleep patterns affects our health, particularly cancer. But first, a look backward.
Despite our desire to shape a schedule to our convenience - to "burn the candle at both ends," if the spirit moves us-our bodies do have a built-in biological clock. This is the source of our circadian rhythm. The word "circadian" is derived from two Latin words, "circa" and "dies," which mean "about a day." Circadian refers to any process that shows a rhythmic behavior, especially a biological process, with a periodicity of 24 hours. Our biological clock is a natural pacemaker in the hypothalamus of the brain.
The first observation of a circadian rhythm in nature is said to be by a Greek geographer of the time of Alexander the Great, Androsthenes of Thasos. He described the diurnal leaf movements of the tamarind tree (Bretzl 1903). The first modern observation was by de Mairan, in the 1700s, who observed that clover leaves move even in total darkness. The famous botanist Carl Linnaeus (1707-1778) introduced the "flower clock," which works on circadian principles. In 1918, an otherwise unknown J.S. Szymanski showed that goldfish maintain 24-hour activity patterns, even in the absence of external cues, such as light and temperature changes (Danchin 2008).
Since 1994, circadian rhythms have been detected in microscopic one-celled organisms, such as cyanobacteria, which adds a kind of global dimension to the phenomenon. These blue-green algae have an internal clock that turns on two-thirds of its genome in the morning, and the other one-third in the evening.
For billions of years, life evolved to accommodate a simple day-night rhythm. During all that time, the only source of illumination was the sun, moon and stars, plus an occasional meteorite, volcano or firefly. Then, just a few hundred thousand years ago, hominids learned to control fire. This led to campfires, torches, oil lamps and candles. A relatively few of our busy ancestors may have "burned the midnight oil" to extend their work or study day, but most common folk went to bed with the setting sun and rose at the first hints of dawn. That was the rhythm of life. An aerial, nighttime view of the world at that time, had it been possible, would have shown almost complete darkness.
Then about 150 years ago, humanity learned to harness electricity. The first US electric power plant was built in 1882 but as late as 1930, only 10 percent of American rural homes even had electricity. The Rural Electrification Administration (REA) of 1935 started to change that. In a New England village that I know well people still speak of the northern end of town as the "dark side." At first I thought this referred to their low morals, but later learned this part of town did not get electricity until the 1930s.
To summarize then, our ancestors - from the beginning of one-celled life on earth until just yesterday - lived by the natural rhythm of the astronomical bodies, occasionally supplemented by some burning wood or whale oil.
Today, as satellite pictures readily show, much of the world is brightly illuminated night and day. In many areas, it is increasingly difficult to find true darkness. Light pollution rules the globe. Every night across America there are 300 million business lights, city lights and streetlights burning that serve no particular purpose except to publicize the existence of various commercial enterprises. Much of this use is frivolous at best, and does not increase one's safety or security, but it does block out the view of the night sky and causing various annoyances and hazards.
Light pollution is not just a constant annoyance but is governmental policy in many localities. We are now in a situation unimaginable to our biological ancestors. We stay awake for as long as we want, surrounded by street and store lights, home illumination, ever-larger television and computer screens, etc. Some of the street illumination creeps into your bedroom when you try to sleep. If you then have trouble sleeping, America has a cure for that too. Zolpidem (sold here as Ambien), one popular sleeping pill, had annual sales last year of $12 billion! This is a common, but hardly a normal, situation.
In previous decades people were thrilled to get electricity into their homes. Few people stopped to consider the subtle biological effects that this development might have on their internal biological clocks. Scientists are beginning to figure out what the long-terms effects might be, and some of them are very worried. Next week I will discuss the relationship of light-at-night to the elevated rates of cancer and other diseases.
Kondo T, Tsinoremas NF, Golden SS, Johnson CH, Kutsuna S, Ishiura M., Circadian clock mutants of cyanobacteria. Science. 1994;266(5188):1233-1236.
Danchin, Antoine. Important Dates 1900-1919. HKU-Pasteur Research Centre (Paris).
Here are some more reflections on the fascinating "Circadian Disruption and Cancer" conference that I attended at the New York Academy of Sciences a few weeks ago.
There are a number of reasons to suspect that poor sleeping habits contribute to an increased risk of breast or prostate cancer. Prime evidence for this comes from a Norwegian study showing that totally blind women have a decreased risk of breast cancer compared to sighted women. The effect was only seen in the totally blind, as there was no such protective effect from any degree of sight disability other than total blindness.
Using Norway's large cancer registry, the authors identified 296 blind women. Their incidence of breast cancer was just 64 percent that of sighted women, i.e., there was a 36 percent protective effective. But among those who went blind before the age of 54 (and therefore had lived in total darkness for a longer period of time) the breast cancer incidence ratio was just 0.51. In other words, their breast cancer risk was half of the sighted women (Kliukiene 2001). That's an extraordinary reduction, which sparked considerable discussion among researchers at the conference.
"Our findings give support to the 'melatonin hypothesis'," the Norwegian authors said. In other words, it supports the idea that the hormone melantonin is protective against breast cancer. A Finnish study found a similar effect among men with prostate cancer (Pukkala 2006).
So what is this "melantonin hypothesis" of which the Norwegian speak? Melatonin is a hormone naturally produced every day by the pineal gland, which is located deep in the brain. Healthy young and middle-aged adults generally secrete about 5 to 25 micrograms of melatonin each night. This amount tends to decline with age, and this decline is possibly linked with an age-related rise in sleep difficulties.
Melatonin is sometimes described as the sleep hormone, but this is not correct. It is not geared to the sleep cycle, although it may help you fall and stay asleep. It is produced in the dark, regardless of whether or not the person is sleeping. Hence its name, which was coined in 1958 from the Greek word, 'melas,' meaning 'black.' Theoretically, you could be up and about in the dark (such as listening to the radio) and still produce the normal amount of melatonin.
At dusk, the decrease in sunlight sends a signal that stimulates the pineal gland to produce more melatonin. Hormone levels then continue to rise steadily for hours, peaking at around 2 a.m. (3 a.m. in older people). It then declines sharply as morning approaches. By 8 a.m. or so your melatonin levels are back down to their typical low daytime point, only to start the cycle over again the following evening.