Sun, Nov 07, 2004 - Page 9 News List

The human body clock

Alive and ticking - Did you know that your lungs are more effective in the afternoon, your brain power peaks around noon and your sex drive is at its best just before 10pm?

By Joanna Moorhead  /  THE GUARDIAN

ILLUSTRATION: YENTSUN CHOU

Try this: work early in the day, and tackle your trickiest conundrums around noon. Do yoga or pilates at around 5pm, followed by a workout or swim. Have a glass of wine or two with an early dinner at around 7pm, and skip the TV news at 10pm. Instead have a long, relaxing massage, ideally followed by lovemaking.

Why? Well, according to experts, our body's systems are governed by circadian rhythms that repeat in 24-hour cycles -- which means we can time our behavior to ensure our body is best primed to deal with what we're asking of it. So morning is best for work because our short-term memory, logical reasoning and concentration peak then: yoga is good in the afternoon, because that's when our bodies are at their most flexible. In the late afternoon, body temperature peaks -- some experts say this is a "natural warm-up" for exercise. Your digestive system and your liver are at their best around 7pm, and skin sensitivity and libido are highest at around 9:30pm.

Researchers are finding out more all the time about the ebb and flow of the human body. Last month a new study from Long Island Jewish Medical Center found that lung function peaks in the late afternoon: another reason why it's good to exercise then. Nearly 5,000 patients were analyzed, and the findings presented to the American College of Chest Physicians were that lung function is at its least effective around midday, and at its best between 4pm and 5pm.

This has implications for more than just when you go to the gym. What lung specialists are excited by is the possibility of timing medication so that it is given at a time when it can penetrate the respiratory tissues as effectively as possible. Asthma medications, for example, could be more effective in the late afternoon, and many patients who deliver bronchodilators round the clock could find they get the same effects with a lower dose if their drugs are time -- targeted.

It might also, says Long Island researcher Dr Boris Medarov, be better to extubate patients who have been on ventilators in the late afternoon, when their lung function will be at its best and they may be better able to breathe on their own.

It's the fine-tuning of drugs to the body's natural rhythms that is behind much of the current research in the field.

"There are big possibilities," says science writer Leon Kreitzman, co-author (with Russell Foster of Imperial College, London) of Rhythms of Life, a book about our daily rhythms.

"We're learning more all the time about when is the best time to administer drugs. In the field of cancer, for example, where the drugs are very powerful, it's especially significant. What you want to do with cancer drugs is hit the tumor cells when they are dividing -- the problem is, you're also hitting other areas of the body with dividing cells, such as the hair and the gut. That's why people having chemotherapy so often lose their hair and feel sick. If we could find a way of timing chemotherapy more effectively, we might be able to give the drugs at a time when the tumor cells are dividing, but when the hair cells and the gut cells are not, and so reduce the impact on those areas," he said.

Not all the reasons why certain systems work best at certain times are fully understood, but in general, said Foster, what the research tends to show is that the human body's rhythms are linked to two external factors: light and temperature.

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