Natural Light: A Missing Ingredient for Health?

Over the past decade, researchers in the fields of medicine and public health have been discussing, with increasing frequency and alarm, the ongoing increase in obesity, diabetes, and other chronic diseases, despite advances in technology. We often use the term “lifestyle disease” to highlight the role of diet, exercise, and stress in the etiology of these conditions.

But what if technology itself is a risk factor for chronic disease? What if our increasing reliance on computers, smartphones, and the Internet is undermining our health, apart from the way these devices keep us sedentary?

I recently had the opportunity to speak on a panel at the Library of Congress on the role of lifestyle in healthy aging. One of the copanelists was Dr. Eugenia Ellis, an architect and researcher at Drexel University who is examining the effect of artificial light on sleep, endocrine regulation, and chronic disease. She discussed the relatively recent discovery of light-sensitive cells in our retina called ipRGCs (“intrinsically photosensitive retinal ganglion cells”) that are largely separate from visual perception. These cells, which comprise only about one percent of the retina, communicate directly with the hypothalamus and play an integral part in regulating our circadian rhythms.

It has long been observed that shift workers and others who sleep during the day and stay awake at night are at increased risk for diabetes, cardiovascular disease, cognitive impairment, and even certain cancers. But why? What is the mechanism that explains how disruptions in sleep/wake cycles impact health?

Dr. Ellis explained that, over the course of a day, there is a natural shift in the pattern of light that directly affects how our circadian clock is “set.” In the mornings and evenings, as we move first out of and later into sleep, natural light is shifted toward the red end of the light spectrum. During the middle of the day, when light is brightest, it is blue-shifted. This pattern of light-shifting could directly determine critical variations in the levels of specific hormones, such as melatonin and cortisol, that regulate sleep, insulin release, metabolism, and other functions.

Here’s where technology enters the picture: Artificial light—from an LED lightbulb, computer screen, smartphone, or TV—is largely blue-shifted. So when we are surrounded by artificial light in the evening, be it in our work environment or watching late-night TV or Internet surfing, our internal clock is being told that it’s midday. No wonder so many people have trouble falling asleep at night. This disruption in the natural light cycle can lead not only to insomnia, itself an increasingly common disorder, but also to the hormonal and metabolic disregulation that promotes obesity, diabetes, and cardiovascular disease.

What can we do to avoid this disturbance in our biological clock? We can make sure we’re exposed to natural bright light during the middle of the day (by taking a walk at noon, for example) and avoid artificial blue-shifted light in the evening and late at night. Simple changes can make a huge difference, such as using dim or red-shifted lights in our bedrooms, turning off the TV and computer after 8:00 pm, and not keeping your phone by the bed for late-night texting. (Apple recently released a software update for iPhone, called Night Shift, that lets users adjust the display away from blue spectrums of light at night, but it has not yet been tested by researchers.)

Ayurveda, India’s traditional “science of life,” has long advocated the importance of adhering to our natural rhythms to support and maintain good health. The role of natural light in regulating our circadian rhythms, and therefore our metabolic health, is just one more example of how Western science is validating ancient wisdom.

© Kripalu Center for Yoga & Health. All rights reserved. To request permission to reprint, please e-mail

Lisa B. Nelson, MD, is a family practice physician, Director of Medical Education for Kripalu programs, and a Kripalu faculty member who has trained thousands of individuals in mind-body practices for health and vitality.

Full Bio and Programs