Enter the Chronotherapists
By OLIVIA JUDSON
Here’s my prediction for the Next Big Thing in health care: chronotherapy, or therapy by the clock. Yes, in the future, your medicines, your operations, your mealtimes and when you step onto the treadmill or the badminton court — all will be overseen by your personal chronoconsultant.
It’s been known for ages that our bodies have daily, or “circadian,” rhythms. Body temperature is lower in the morning than it is in the afternoon. Blood pressure is low during the night, and rises just before you wake. Muscles are stronger in the afternoon than they are in the morning, and you may have greater dexterity then, too. Badminton players tend to serve more accurately in the afternoon, for example.
But now it’s clear that the body clock is in charge of many other, more subtle processes as well. The content of human breast milk changes during the day. Evening milk is full of compounds that make a baby sleepy; morning milk isn’t. The liver, too, has a strong daily rhythm: many of its activities shut down during the night. Levels of several hormones, including melatonin (involved in sleep) and ghrelin (involved in appetite), rise at night. Testosterone, in contrast, is highest in the morning and lowest in the late afternoon. Cholesterol is made more rapidly at night. Even cancers have a rhythm: breast cancers, for instance, grow faster during the day.
The implications of all this are huge. Living against your body clock — as so many of us do — can affect your health and well-being in myriad ways. Some of these are trivial: unless you’re professional (or super-competitive), it probably doesn’t matter if your badminton serve is a little off in your morning games. Besides, your opponent’s will be, too. (It may, however, be better for your heart if you play in the afternoon.)
But living against the clock can also lead to major health problems. Obesity, breast cancer and certain kinds of mental illness are all associated with circadian disruption.
Disruption can be a consequence of shiftwork or jetlag — or of not spending enough time sleeping, or in the dark. Darkness is important because even a brief exposure to light during sleep-time can be enough to reduce melatonin levels and reset the body clock. Exposure to light in the night has been linked to breast cancer; consistent with this, women who are totally blind have a lower incidence of breast cancer than those who can see even a little bit.
Badly timed light isn’t the only troublemaker. Eating at the wrong moments — like the middle of the night — makes it harder for the body to process food and leads to weight gain. A recent experiment shows this nicely. Two groups of mice were fed identical diets but on different schedules: one group was allowed to eat only during normal waking hours, while the other was restricted to eating during normal sleeping hours. After six weeks, the mice allowed to eat only during sleep-time were significantly fatter than the wake-time eaters — a result that may help explain why obesity is so common among shift-workers who, because of their jobs, are forced to eat against their clocks.
In fact, sleep itself has been implicated in obesity: not sleeping enough is associated with getting fat. (Which suggests the sleep diet: stack those Zs and see the pounds melt away!) More worrying: obesity may actually interfere with the clock mechanism. In mice, the genes involved in regulating the body clock function differently in obese animals as compared to thin ones: the clocks of obese animals are less rhythmic. Perhaps, then, one way to treat (or prevent) obesity would be to impose a strong circadian rhythm on mealtimes and bedtimes.
To my knowledge, chronotherapy has not yet been tried for obesity; but it has, with great success, been used in psychiatry. Several mental disorders, including bipolar disorder, can be rapidly ameliorated by a resetting of the body clock. Indeed, it’s been argued that manipulating the body clock affects the same parts of the brain as antidepressant drugs — but that chronotherapy works faster and with fewer side effects.
Even conventional medicines work better when the body clock is taken into account. For example, evidence suggests that some statins — drugs that help people reduce their cholesterol levels — are more effective when taken before bedtime. Several of the drugs used in chemotherapy also have a “best” time of day: give the drug at the right moment, and you can take a smaller dosage, get a greater benefit and have a lower risk of unpleasant side effects. Sounds good. But don’t forget: regular good sleep in a nice dark room can inhibit tumors, and may thus help you avoid chemo in the first place.
Much more, no doubt, remains to be discovered, and it may, in fact, be a while before a chronotherapist opens an office near you. (That’s often the nature of the Next Big Thing — you see it on the horizon ages before it arrives.) But while we’re waiting for medicine by the hourglass, there are still steps that can be taken. I don’t know about you, but I’m going to darken my bedroom, cancel the midnight feasts and put sleep at the top of my list of things to do. It’s about time.
Thursday, December 24, 2009
Dad Was Right Again!
Oh dear. So my late hours, late dinners (I work until 8-9 a lot of the time, with only five minute breaks between classes), and ability to sleep with the sun pouring through the window (no curtains, but then I love waking up to sunlight) are probably not things to celebrate. Sigh. I suppose I could try making 2010 the Year of Health.