Cycles of Life

Little fluctuations in the daily rhythms of the human body can make a big difference when it comes to health

FOR THE PAST 40 YEARS, Bob Sothern has been the guinea pig in a medical test of his own making. Five times a day, he stops whatever he’s doing to measure his temperature, blood pressure, heart rate, respiration, and several other biological functions. He also charts his mood, time perception, hand-eye coordination, and physical vigor. He then records all the data for later analysis.

It’s a tedious routine, but one that has become second nature to Sothern, a research associate in the College of Biological Sciences at the University of Minnesota. He’s a pioneer in the field of chronobiology, the study of the body’s internal biological rhythms and their effect on health. Though ignored and belittled for many years, chronobiology is today a respected and rapidly expanding area of scientific research.

Most of us are vaguely aware of our internal timekeepers. You may have more energy or a brighter mood at certain times of the day. You may feel out of sync when you fly across time zones or switch to the night shift. You probably identify yourself as a “morning” or “evening” person: The former are most alert and productive during the late morning hours, while the latter feel they are at their best after 6 p.m.

Understanding the subtle pattern of changes that our bodies undergo daily can tell us a great deal about our health. Take body temperature: It was once believed humans had a fixed, “normal” oral temperature of 98.6 degrees Fahrenheit. In fact, body temperature often fluctuates by as much as 3 degrees in the course of a day. It plunges to rock-bottom during the early morning and peaks late in the day, with a small dip during the “siesta” hours of early afternoon. So if you’ve got a temperature of 98.6 degrees at 7 a.m., it may mean you’re coming down with the flu, while a temperature of 99.4 degrees at 3 p.m. may be nothing to worry about.

The stress hormone cortisol also follows a daily pattern—one in direct opposition to that of body temperature. “It should be sky-high in the morning and quite low in the evening,” says Sothern. If that pattern goes askew, it could mean you have an adrenal-gland illness, such as Addison’s disease or Cushing’s syndrome.

In recent decades, Sothern and other chronobiologists have uncovered the importance of these rhythms in the prevention and treatment of disease. They have found, for example, that the time of day when cancer drugs or radiation therapy are administered may play a significant role in the success of the treatment. In one study, the eight-year relapse rate for children with leukemia was more than twice as high for youngsters who took their chemotherapy meds in the morning rather than in the evening. Research has also shown that commonly prescribed asthma medications are both more effective and safer when taken at certain times of the day.

Chronobiology’s findings are not yet widely applied by physicians and other health professionals, but that is changing as new technology makes tracking rhythms less burdensome. Later this year, a Minnesota-based project will enable people around the world to more easily monitor their blood-pressure rhythms. Researchers hope the data will help patients and doctors identify signs of heart disease long before more traditional symptoms appear.

THE SCIENCE of chronobiology was “invented” by Franz Halberg, MD, co-director of the Halberg Chronobiology Center at the University of Minnesota. In the late 1940s, Halberg, then a young research fellow from Romania, chronicled how the number of white-blood cells in laboratory mice dramatically rose and fell in a predictable daily cycle. He dubbed that cycle circadian, from the Latin for “about a day.” Soon he was finding other rhythms and exploring their implications. He observed, for example, that when mice were exposed to extremely loud noise at 10 p.m.—their most active time of day—they were susceptible to seizures. But when a similar group of mice was exposed to the noise at noon—their rest cycle—no seizures occurred.

For many years, Halberg’s work was widely ridiculed. But gradually, he and his colleagues have won over the scientific community, proving that virtually every biological function in humans, including body temperature, heart beat, and blood pressure, conforms to a daily, weekly, monthly, or annual rhythm.

Still insatiably curious at 87, Halberg has recently documented the effect of solar wind, sunspot, and geomagnetic cycles on the human body. He’s found, for example, that a significant spike in the incidence of heart attacks occurs in sync with each 10.5-year cycle of solar activity. (The next peak is expected in 2011-2012—and NASA predicts it’s going to be a big one.)

Halberg is on a crusade to get people to monitor their blood pressure rhythms. “If we do not monitor our blood pressure, we ‘fly blind’ ” in terms of knowing the true state of our health, he says. Blood pressure can vary over the course of a day by as much as 30 percent. So if you have your blood pressure checked when your cycle is at its zenith, the reading may indicate a health problem that doesn’t exist. Or, worse, the reading may lead your doctor to overlook a problem that does exist.

RECORDING your heart beat, temperature, and blood pressure—for a few days every few months is a great first step in maintaining health and preventing disease, says Sothern. He recommends three simple tools: a wristwatch (to time your heart rate), a thermometer, and a blood-pressure cuff. If you record the information and plot it on a simple chart, you’ll recognize your individual pattern. You should discuss this information with your doctor if it changes.

Halberg hopes charting such biological rhythms will soon become even easier. Several years ago, he called on engineers to develop tools that would make it less cumbersome for people to track their blood-pressure rhythms. That call-to-action was answered by software engineer Larry Beaty and the Twin Cities chapter of the International Institute of Electrical and Electronics Engineers (IEEE).

The aim of the Phoenix Project, as Beaty and his fellow volunteers dubbed their endeavor, is to build a low-cost blood-pressure monitor that can be worn around the clock, charting blood pressure, heart rate, and, perhaps, blood-flow rhythms. In addition, the engineers are developing software that will allow users to not only plot and calculate their time-adjusted average blood pressure, but also to compare data with others. Participants will be asked to check their blood pressure at least once every week for a year. (If you want to be notified by e-mail when the project is ready to launch, register at And you don’t have to have high blood pressure to sign on to the project. “From a research prospective, we need healthy people, too,” says Beaty.

Understanding blood-pressure patterns may help you and your doctor  evaluate health information. A year ago, when Sothern went for his annual medical checkup, his blood-pressure reading seemed unusually high. Because Sothern had kept records, he knew it was exactly 10 points higher than usual for that time of the day. He attributed the increase to stress: At the time, he was working hard to finish a textbook on chronobiology.

“That book almost killed me,” says Sothern, laughing. “It took a year for my blood pressure to come back down.”

He should know. He has the data to prove it. MM

Susan Perry is a frequent contributor to Minnesota Monthly.