If You Only Take One Daily Walk, Make Sure It's In The Morning — Here's Why

Our light sensitivity is at its lowest when we first wake up, meaning we need a bright blast to alert our brain and to set our circadian rhythms for the day. Numerous studies have shown that how we spend the first hour of waking can make or break our chances of a good night's sleep. Morning light tells the layer of neurons behind our eyes that it's time to get going, ensuring that our production of melatonin (the hormone that makes us feel drowsy and helps us sleep at night) eases off. But a shock of morning light also sends cortisol flooding through our bodies—waking us up, energizing and invigorating us. Ideally, a few minutes of our morning walk should be without sunglasses, unless it's a dazzlingly bright day.

Morning light has the potential to do far more than wake us up and help us sleep. An early-morning walk could also protect our hearts: A recent study suggests that bright light can protect and enhance our cardiovascular health3 by boosting a specific gene that strengthens blood vessels and cuts our risk of a heart attack. Scientists had already spotted a link between light and heart disease, noting the greater prevalence of heart attacks during winter months. But this study revealed something intriguing: Participants exposed to 30 minutes of intense light between 8:30 and 9 a.m. for five consecutive days had raised levels of a protein called PER2. PER2 is critical for setting circadian rhythms, improving metabolism, and fortifying blood vessels. Earlier versions of the same experiment on blind mice found bright light had no effect, hinting at the crucial role our eyes play. 

It's not only our circadian rhythms that benefit from an early-morning walk. A 2012 study found that women who took a brisk 45-minute walk at 8 a.m. every day were more active for the rest of the day. They were also less responsive to pictures of food. This was one of the first reports to establish that exercise energizes us while simultaneously—and a little perversely—suppressing our appetite. Some researchers now think we eat less after exercise because brisk movement raises our body temperature, activating hypothalamic neurons, which help us control food intake. Just as we eat less when it's warm outside, so we eat less when our bodies are warmed by walking.

After 14 years of walking dogs and children every morning, I found myself addicted to a start-of-the-day romp. Now, like Martineau, I appreciate the opportunity to collect myself, to plan my day: The health benefits are a serendipitous byproduct.