Our biorhythms are governed by powerfully precise timekeeping cells found throughout the body. The body has a master biological clock, which keeps the body’s other clocks in sync. This master bio clock relies heavily on external cues of light and darkness, delivered along a pathway that travels from the optic nerve.

What’s your chronotype?

Our biological clocks function genetically. From one person to another, clocks run slightly shorter or longer based on the PER3 gene. People with shorter clocks prefer morning-centric activity, while those with longer clocks are skewed to later in the day. The preferences for “morningness,” “eveningness,” and “in betweenness” can be identified as chronotypes. My clinical experience has shown me an additional type — the troubled sleeper, or the insomniac. Based on your chronotype, there are biorhythms (often based on hormone fluctuation throughout the day) attached to everything you do: sex, communication, emotionality, work — even having fun.

“Paying attention to bio time can make you happier in your personal life and more productive and successful at work.”

However, social time and biological time exist in deep conflict. Work schedules misalign with chronotypes, particularly for the millions of people who perform shift work. School start times are aggressively opposed to the biorhythms of young people, who generally move into late-leaning during their teenage years and early 20’s. We skip breakfast (but load up on caffeine) and snack late into the night, throwing our digestive rhythms wildly out of sync and endangering our metabolic health.

Change your timing

In the past 15 years, there has been a landslide of scientific data indicating a relationship between chrono-misalignment and the major diseases of our time: cardiovascular disease, obesity, diabetes, depression and cancer. The Power of When goes beyond disease onset and prevention. Paying attention to bio time can make you happier in your personal life and more productive and successful at work.

Bio time points us toward the best times to make a sales pitch, to negotiate a deal or to ask for a raise. Bio time guides us to the best times for exercise, social time with friends and serious conversations with our kids and our partners. Want to add vigor to your sex life? Rethink your bedtime sex habit. For most chronotypes, morning — when sex hormones reach their 24-hour peak — is an ideal time for sexual activity. The worst time? After 11 p.m., when those same hormones reach their daily nadir. Perhaps the best news about bio time is that with awareness and attention, it’s possible to make simple changes to the “when” of living that can have a transformative effect on health and well-being.