Early bird or night owl? Blood test reads personal body clock

Are you an early-bird-gets-the-worm kind of person, or do you need a bulldozer to shove your head off the pillow each morning?

Scientists in Japan say they can tell the setting of your body’s circadian clock just by examining a small blood sample.

In a report published Monday in the Proceedings of the National Academy of Sciences, researchers said they have developed a convenient method of estimating an individual’s personal body time by examining the concentration of hormones and amino acids in two blood samples taken 12 hours apart.

The development could carry great benefit for those who are dieting, or taking medication with severe side effects: Certain anti-cancer drugs are most potent when taken at specific body-times, and toxic at others.


Internal body time refers to the molecular time-keeping mechanisms that regulate the sleep, digestion and metabolic processes of all mammals.

While scientists have long known that personal body times can vary by as many as 12 hours between individuals -- the difference between a so-called morning lark or night owl -- they have found it difficult to determine an individual’s exact circadian clock setting. The current method is invasive and time-consuming -- medical workers must draw a person’s blood on an hourly basis for up to 24 hours, and track levels of the hormone melatonin.

The study’s lead author, Takeya Kasukawa, a genomicist with the RIKEN Center for Developmental Biology in Kobe, Japan, wrote that the new method examines the level of 50 different metabolites and compares them to a timetable. Blood must only be taken twice in a 24-hour period. The method pinpoints personal body time to within three hours, the authors wrote.

The study, and formulation of the timetable charts, was based on the observation of six healthy male volunteers in their 20s.


An individual’s circadian rhythm can be altered by shift work, jet lag or an irregular lifestyle. Determining a person’s body clock setting is important for the administration of medicine, and researchers said it could also have in impact on weight gain and dieting.

Studies with mice concluded that the animals got fatter while eating at the wrong time for their circadian rhythms. “These results suggest that food intake at different body times can alleviate or exacerbate diet-induced obesity,” those authors wrote.