Morning Rays Could Improve Your BMI?--Voodoo Science or the Real Deal?

As I was scouring the "webosphere" (yes, I just made up that word), I came across an interesting bit of research recently published on Plos One. The article, written by Kathryn J. Reid et al., was revealingly titled "Timing and Intensity of Light Correlate with Body Weight in Adults." I could hardly pass up the opportunity to take a look, and the information I gleaned from the study proved interesting to say the least. In case you hadn't gathered from the study's title what the authors' thesis was, here's a short synopsis: The authors, essentially, conclude that exposure to light in the early hours of the day correlates with lower bodyweight in adults.


This is an interesting thesis indeed! So let's take a look....

The All-important Circadian Rhythm

It should come as little surprise that circadian rhythm--the natural rhythm of your body's hormones in response to environmental stimuli, such as light--plays a major associative role in relation to bodyweight, health, and stress. In relation to bodyweight, one's circadian rhythm is highly determinate of one's sleeping and eating patterns. Because of the nature of circadian rhythm's importance, the authors of this study, understandably, felt quite compelled to examine some important factors related to its regulation.

As the authors indicate--

"Light exposure can influence sleep and circadian timing, both of which have been shown to influence weight regulation."

What Happens When Circadian Rhythm Ain't so Rhythmic?

When one endures a rather unnatural circadian cycle--denoted by little sleep and by going to sleep at late hours--odds are, you might very well have a higher BMI (except if you're my roommate who's 6'2", 140 lbs, and who doesn't go to bed until 3-5 AM, and who barely gets 4-5 hours of sleep on a regular basis!) [1, 2, 3, 4, & 5]. Baring the unusual (and perturbing) case of my roommate, for the typical human being, I'd say it's a fairly good idea to get to bed at a decent hour and, moreover, to sleep for whatever duration you require in order to awaken spontaneously in the morning, feeling totally rested [6].

What Reid et al. Discovered

The authors conclude their study thus--

"In conclusion, the findings of this study indicate that the temporal pattern of light exposure during the daytime can influence body weight independent of sleep timing and duration."

There are, however, some important caveats of which to take note.

Noteworthy Thing #1

For instance, the authors state--

"Our results suggest that the relationship between light and BMI is not simply a function of the accumulated minutes of light during the day, but more importantly the temporal pattern of light exposure above a biological threshold."

Therefore, the correlation between light exposure and lower BMI arises in the context of a particular intensity, duration, and timing of light exposure. Levels of about 500 lux earlier in the day were most associated with lower BMI.

Noteworthy Thing #2

The authors also point out--

"It is also possible that the natural changes in the intensity and wavelength composition of light in the morning compared to the afternoon/evening may in part explain our finding for a differential effect of earlier vs. a later daytime light exposure pattern and BMI. For example, there is generally a higher amount of blue light (shorter wavelength) in the morning. (*)Blue light has been shown to have the strongest effect on the circadian system, including the suppression of nocturnal melatonin secretion."

It makes some sense, then, why getting light exposure earlier in the day proves beneficial for BMI, while exposure later in the day, or in the evening or at night, has the opposite effect. Interestingly, though, the authors of this study did not find any correlation between later light exposure and higher BMI (much to the author's surprise). Nevertheless, numerous other studies do demonstrate such a result.

Noteworthy Thing #3

The authors also noted, and rather unexpectedly, that sleep duration had little to do with BMI, at least within their own experiment--

"...unlike previous reports, the timing of sleep was not directly correlated with BMI in this study."

Despite this finding, however, other evidence suggests that sleep duration may indeed be an important factor in predicting/controlling BMI, via sleep duration's effect on leptin and grhelin [7].

Noteworthy Thing #4

In another interesting turn of events, the authors also discovered--

"...that changes in the timing of light exposure were associated with body weight independent of caloric intake."

This finding is interesting, to say the least. It may be, however, that, as the authors suggest--

"...light exposure history during the day can alter nocturnal levels of melatonin and sensitivity of the circadian clock to light. These effects of light may play a role in metabolism and weight regulation."

In particular, consider the inverse relationship between melatonin levels with insulin/insulin sensitivity [8], or the fact that low melatonin levels are associated with type 2 diabetes [9].

Noteworthy Thing #5

There's yet one more little thing for us to consider regarding this study--

"The limitations of this study include lack of random selection from a nationally representative sample and use of self-reported diet and BMI which may have resulted in measurement error."

In other words, the results gleaned from this study could be total BS, if it should turn out that the study's participants were dishonest in their self-reporting, which could be a very real possibility.

So What Have We Learned?

YES PLEASE!

All things considered, I'd say the authors' primary thesis checks out--in any event, even if the authors' thesis is wrong, it wouldn't hurt to get some quality blue light early in the day any way. Some evidence suggests that blue light might actually be as effective as coffee at waking you up in the morning by giving your brain that oft needed kick in the rear to get going [10].

In light of the evidence, here are my suggestions: (1) get quality sleep; (2) go to sleep at "normal" human hours; (3) get some exposure to blue light earlier in the day, and avoid blue light exposure as much as possible prior to going to bed.

Seems pretty simple to me.

Enjoy your Sunshine! (it's pretty gloomy where I am right now)

(*)The effect of blue light exposure on melatonin secretion is one important reason why I down-loaded f.lux software onto my computer. F.lux is a program that automatically shifts the color of your computer screen from blue light dominant to red light dominant whenever the sun goes down, thus preventing the suppression of nocturnal melatonin later in the day.