Does daylight-saving time mess with your internal clock?

Health and medicine explained.
Nov. 1 2007 7:34 AM

Your Health This Week

Does daylight-saving time mess with your body's internal clock? And more.

Dr. Sydney Spiesel was online on Nov. 1 to chat with readers about this article. Read the transcript.

This week, Dr. Sydney Spiesel discusses the disruptive effect of daylight-saving time on the body's internal rhythms, what happens when you accept a health-related spam offer, and the best ideas for improving the health of the world's poor.

The downside of daylight-saving time?

Illustration by Mark Alan Stamaty. Click image to expand.

Question: After midnight next Sunday, the clocks where you live will move backward by one hour to shift an hour of daylight from afternoon to morning over the next four winter months. You will share this experience of daylight-saving time with about one-quarter of the people on Earth. What happens to your body's internal clock when it is suddenly reset by society's clock?

Context: The body's daily cycle of activities—the circadian rhythm—determines when we are sleepy and alert, when we want to eat, and even when we produce less urine so our nighttime sleep will be less interrupted. Though there is a spectrum of preferences, from "larks" to "owls," the internal clocks that set our circadian rhythm are mainly regulated by the time the sun rises. (Here's how to figure out which kind of bird you are.) We are not consciously aware of this dependency, and our time of awakening is often affected by external forces, like the need to get to work on time. Chronobiologists, the scientists who study our internal clocks, correct for these effects by comparing awake and asleep times on work days and free days. They have found that the relationship between the arrival of dawn and the midsleep point—the time halfway between the moment you fall asleep and the moment you wake up—remains constant, even as the time of sunrise changes when the length of the day varies with the seasons.

Study: A new German study uses this predictable relationship to study what happens to our internal clocks when the external clocks jump an hour forward or backward. Drawing from a database of 55,000 Central European subjects who submitted daily sleep records, they showed that the normal correlation between dawn and the sleep cycle becomes disrupted during the transition to daylight-saving time.

Findings: In an effort to clarify whether this change was due to the changed clock or to some other phenomenon, the authors zeroed in on the sleep-wake and activity cycles of 50 people during the weeks around the spring and autumn leaps forward and back. They found that the spring institution of daylight-saving time was exactly the moment when the coming of dawn disconnected from the body's sleep-wake cycles. When standard time returned in the autumn, the body's circadian rhythm again linked itself to the time of sunrise.

Conclusion: Practically speaking, what does this mean? If, as some recent research has suggested, sleep and psychiatric illness may be closely tied, perhaps the sleep disruptions associated with time changes might affect the incidence of psychiatric disease during the transition periods. An early study suggested that this was, indeed, the case; more recent research on patients with depression casts doubt on the association. There is clear evidence of a spike in car accidents associated with the spring transition to DST and the fall transition back to standard time. I am tempted to think that disturbances in circadian rhythm are the cause.

Question: Roughly one out of three pieces of e-mail spam is devoted to "medicine"—a nutritional supplement purported to enhance health or quality of life, a cheap prescription order, or, of course, the ubiquitous offer of treatment for erectile dysfunction. Do these sites actually deliver? And if they do, are the goods that arrive pure, safe, and effective?

Study: Peter Gernburd and Alejandro Jadad of the University of Toronto set out to answer these questions by setting up three slightly different Internet e-mail accounts in Canada. They got more than 4,000 unsolicited messages in November 2006, one-third of them health-related. Three weeks later, with some trepidation, the researchers ordered one of every product offered.

Findings: Most of the Web sites attached to the spam had vanished within the three weeks since the messages were sent. The authors were left with 19 Web sites with 27 offers of prescription drugs or natural health products. They found no evidence that the sites abused the credit card information they sent. But the majority of orders were unsuccessful. Sometimes the site stopped working, and sometimes it did not process the order. Arrival stats for prescription medications:

  • Erectile dysfunction treatments: one out of five arrived.
  • Controlled drugs with addiction potential: three out of five.
  • A sleeping product and an antibiotic: none.
  • Expensive drugs for arthritis, obesity, heartburn, muscle spasm, baldness, and depression: one out of seven.

Of the natural products, roughly half were delivered. These preparations were largely intended for obesity treatment, erectile dysfunction, and penis enlargement.

Conclusion:The researchers haven't figured out yet whether the products they received were genuine or fake. Please forgive my skepticism, but based on the ingredient list, I am doubtful. In any case, based on this experiment, Internet medication ordering can hardly be recommended, since the majority of products never come.

Question: If you were to do one single thing to improve the health of the world's poorest people, what would it be? The editors of the journal PLoS Medicine posed this question to 26 experts on international health and to four Peruvians in a poor agricultural community.

Answers: Various experts proposed:

  • The development of a vaccine to prevent AIDS.
  • Exclusive breast-feeding for the first six months of life.
  • For tropical Africa, the distribution of free anti-malarial products like insecticide, treated bed nets, and free access to a new class of potent anti-malarial medications.
  • Building infrastructure, like a network of rural roads, so clinics and vaccines could be brought easily to the people who need them.

There was also a strong consensus about the great value of safe water and good sanitation. Some consultants also stressed the importance of basic education, especially for women. And a number of experts pointed out the enormous importance of ensuring food security, meaning "two square meals a day."

The wisdom of that recommendation is reinforced by a recent study of the association between food insufficiency and high-risk sexual behavior in two African countries, Botswana and Swaziland. The researchers, led by Sheri Weiser of the University of California-San Francisco, found that more than one-third of about 1,000 women reported that they hadn't had enough to eat in the past 12 months. For those women, the risk of selling sex for money or resources increased by 80 percent, and the risk of engaging in unprotected sex increased by nearly as much. This study strongly suggests that one of the most important benefits of reducing food insecurity would be preventing the spread of HIV/AIDS.

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