At a recent SunSprite team meeting, we were talking about light and digestion. Is there a connection? As a psychiatrist, I realized I wasn’t sure. It’s not a question I’d ever asked. So I looked. Here’s what I found.

In a series of papers, Hirota, Sone, and Tokura teased out some of the effects of light on digestion. They found that daytime exposure to bright light “exerted a beneficial effect on the digestion of the evening meal” – specifically better digestion of carbohydrates. They found the opposite was true for bright light during the evening meal – dim light (romantic candlelit dinners?) led to better digestion.

Of course, it depends on what you mean by “better.” Bright light with dinner caused “malabsorption” of carbohydrates. So if you ditch the candles and turn on the spotlights, it just might mean that you can finish dessert and not gain as much weight. (That’s not a recommendation, just a question. The answer’s not in yet. And it’s likely to keep you up at night anyway.)

At the following SunSprite meeting, a new worry popped up. No, we realized, we didn’t want to discover any new benefits of bright light. And if we did, maybe we’d be better off not talking about them. What if we started to sound like an old-time snake oil saleman? “Here it is. Bright light. Good for whatever ails you!“ We want to be sure we’re presenting SunSprite with all appropriate scientific evidence.

But underlying the astonishing multiplicity of light’s effects is a simple truth. We evolved in a world of days and nights, light and dark. We are, at our core, “diurnal” creatures. The result is that most of our physiological process have a circadian rhythm to them. And light, filling our world during the day and fading out at night, is the primary regulator of those internal rhythms.

We talked about circadian rhythms in several blog posts: click these links to learn about how light from our screens can disturb our sleep, or how light sets our internal clocks.