Healthy living
Body matters
Clock on to your body's rhythms
It’s noon, so it must be time for a song... Roger Dobson examines research into the way our health is affected by our body clocks and seasonal variations
Midday is the peak time of day for the urge to sing, according to new research, and it’s also a good time to take a pill for easing osteoarthritis pain.
And while late afternoon, around 5pm, is when we are most likely to be happy and whistle, it’s also the worst time of day for cold symptoms, and for accidents.
Research is revealing just how much our everyday lives are influenced, even controlled, by daily, seasonal and other cycles.
Society may have become high-tech, with 24/7 working practices, artificial light, abundant food, and warm clothing and heating, but these cycles still have a major effect.
"Like almost all life on the planet, much of human physiology and behaviour is controlled, modulated or at least fine-tuned by an internal 24-hour timer," says Professor Russell Foster, Chair of the Nuffield Laboratory of Ophthalmology, Oxford University.
Hundreds of aspects of life as diverse as sleep and wakefulness, body temperature, behaviour, blood pressure, digestion, alertness, disease symptoms, memory and reaction times, have been linked to these cycles. Seasonal cycle research has shown too that the month of birth can increase or reduce the risk of developing decades later, a dozen or more diseases, from Parkinson’s and Alzheimer‘s, to asthma and depression.
Two cycles in particular, the 24-hour or Circadian, and the annual or seasonal, have been shown to have wide ranging effects. There is much less evidence for the effects of another, the 29.5 day lunar cycle. Lightness and darkness, and the body’s perception of them, are the main drivers of the changes that occur over the 24 hours period. Melatonin is the hormone that most obviously responds to light and dark, and in some countries synthetic versions of the hormone are prescribed to combat a common problem that occurs when the light-dark cycle gets disrupted - jet lag.
A master clock in the brain, (in the suprachiasmatic nuclei of the hypothalamus area), orchestrates body cells. Hormones, and other chemicals, including cortisol, prolactin, and growth hormones, are among the compounds whose levels fluctuate over the 24-hour day and which play a part in driving the changes that occur. Vitamins, especially A, C, E and beta carotene - whose levels peak at 1am - are also implicated. Changes in body temperature and blood pressure over the 24 hours are also implicated, and a study at Boston University has shown that the heartbeat fluctuations are at their highest at 10am.
But while much is now known about the 24-hour clock, relatively little is known about the driving force behind the seasonal cycle.
Professor Foster says, "We know that there are changes and that the evidence is rock solid, but we have much less knowledge about the mechanisms involved. Many things are likely to be going on. It may be, for example, that seasonal changes in the availability of nutrients influence the occurrence of seasonal disease."
"The seasons to many people only impinge upon the consciousness because of the yearly cycle of Father Christmas, followed by the Easter bunny and then Halloween pumpkins. Yet our biology is affected by the seasons. Seasonally related metabolic status, temperature, and other factors all appear to modulate, in varying degrees of importance, much of our physiology including even the timing of human fertility and birth."
The mechanisms may be unclear, but the research shows that the effects are real. One of the most intriguing are birth effect studies, which show that different times of the year are linked to different risk rates for a number of diseases, from autism to cancer.
Winter and spring babies are also more likely to be bigger and smarter. Research at Harvard and Queensland universities based on more than 20,000 children monitored for seven years, shows big seasonal variations in intelligence as well as weight, length, height, and head size. One theory is that effects on the growing foetus of seasonal variations in diet, hormones, temperature, sun exposure, and viruses and other infections, may be involved.
Being diagnosed in the summer can also increase the chances of surviving cancer. Research based on more than one million cancer patients in the UK shows that those diagnosed in the summer and autumn are likely to survive for longer compared to those diagnosed in the winter. For women diagnosed with breast cancer, survival chances increased by 14 per cent, and for men and women with lung cancer, there was a five per cent lower risk of dying prematurely, according to the research in the
International Journal of Cancer. One theory is that sunlight is essential for the production of vitamin D in the body, and there is evidence suggesting that the vitamin may have a role in stopping the growth of tumours.
The findings that daily and seasonal cycles have an effect on health are also helping in the treatment of a range of diseases. Lack of vitamin D, for example, which may explain some of the seasonal differences in diseases and infections, is being given as a supplement to those at risk. At Winthrop University Hospital in America, for example, researchers have been running a clinical trial looking at whether Vitamin D insufficiency during the winter may cause increased susceptibility to infections, including the common cold and flu. One groups of patients are being given a vitamin supplement, and the others a placebo, and thedifferences in infection rates will be compared.
The research on the daily cycle has fuelled the relatively new discipline of chronomedicine and chronotherapeutics where drugs and other therapies are given at the time of day when they will have the greatest effects or the least side effects.
Painkillers for rheumatoid arthritis, for example, may be most effective when taken after an evening meal. Some cancer therapy has been found to be up to four times more effective when given in the morning compared to the evening, while cholesterol-lowering statins may be best taken at night. Behaviour theory for depression may be most effective in the afternoons because that is the time of day when mood of depressed people is at its highest.
While evidence for seasonal and daily cycles is extensive, research on lunar effects is much thinner on the ground. It’s been found that GP consultations increase during the time of the full moon - and that gout and asthma attacks peak during the new and full moon. Fertility has also been linked to the lunar cycle.
Suggestions that a full moon has an effect on health and behaviour - the so-called Transylvania hypothesis - has been around for centuries, and while some reports have found links, many others have not.
Critics point out that while the moon does have a gravitational effect upon the ocean tides, the idea that it might also affect on the human body, is unlikely. Harsher critics have called it pseudo science. One suggestion is that odd happenings at the time of the full moon are triggered directly not by the moon, but by people’s expectations that something bad will happen to them.
Daily time cycle
5am
Body temperature at its lowest - and early morning libido begins to rise in men.
6am
Pain of ankylosing spondylitis, a type of spinal arthritis, is three times higher and stiffness about eight times greater between 6:00am and 9:00am, than in the afternoon when symptoms were at their lowest.
7am
Bad cholesterol peaks.
8am
The severity rheumatoid arthritis symptoms is about three times higher between 8am and 11 am than at bedtime. Also peak time for nosebleeds.
9am
Low point of the day for people with depression.
10am
A Boston University study shows that heart is most prone to problems at 10am and least prone at 2am. French women who took part in a survey rated their facial skin as being at its best at 10am.
11am
Shorter-term memory is best in the morning and longer-term superior in the afternoons.
12 noon
Time of day when people are most likely to sing. Also a good time for an argument with verbal reasoning at a peak.
1pm
Migraine attacks tend to recur in a 24-hour cyclic manner with a peak around the middle of the day. Risk of a car accident increases.
2pm
Emergency hospital admissions for cancer are at their peak.
3pm
Maximum body temperature is between 2pm and 4pm, making it a good time to exercise.
4pm
Heart rate peaks.
5pm
Time of the day when people are happiest and most likely to whistle. The body’s toleration of alcohol is at its highest, so it could be a good time for a drink.
6pm
Peak time for the pain of perforated ulcers starts in the evenings.
7pm
Pain of osteoarthritis starts to rise and peak between now and midnight.
8pm
Pain of shingles is at its worst.
9pm
Heartburn risk starts to peak. Research studies show stomach acid secretion is two to three times greater between now and 2am than the rest of the day.
10pm
Eczema symptoms worsen.
11pm
Histamine level begins to rise making asthma systems worse at night.
Midnight
There’s a 29 per cent lower risk of having a stroke after midnight and in the early hours, compared to a 55 per cent increased risk during the late morning.
1am
Blood levels of vitamins are at their maximum.
2am
Bowel movements and stomach rumbling at their slowest of the day. Oil production by skin glands between now and 4am is half what it was at noon.
3am
Sleepiest time of the day. Major industrial accidents like the Three-Mile Island Nuclear Plant accident, the Chernobyl nuclear disaster and the deadly chemical release in Bohpal, India, and the Exxon-Veldez oil spill occurred during late night hours.
4am
Blood pressure is lowest - and immune system cells at their highest.
Useful links
- Understand your body clock
- Are you a lark or an owl?
- Tailor-made nutrition to suit your day
- What to do when insomnia strikes
This article first appeared in the February 2009 edition of Saga Magazine. To subscribe, please click here
Information on this site is for interest only and is not a substitute for professional medical advice. You should consult your own doctor about any specific health concerns.
