The Sunshine Study: Does it do your weight good?

A couple of weeks ago I heard a news story which referenced the power of sunshine.  Readers who have met me know that my favorite thing in life is sunshine.  I was delighted to hear that science supports something I knew anecdotally (i.e., by my personal experiences); the sun does a mind good.  It follows that what does the mind good will do the body good (tanning excluded!).

The headlines were even better – tantalizing even… early morning sun aids in weight control… or those who spent time in the sun between  8 and 11 a.m. weigh less (smaller BMI) than those who do not get out in the early sun. REALLY?!  I exercise outside almost every morning (walk, bike, run) after 8am but before 12.  Yay!

I do have a low BMI, but I know it is because of my dietary intake and physical activity (it certainly isn’t my genes), I am not inclined to believe that the sun I adore is keeping me thin.  Still, I wanted to learn more about this study so I could give my favorite ‘element’ the kudos and promotion it deserved.

I located the referenced study – referenced in the popular press and linked for you below – and read every single word.  I read and read, paragraph after paragraph, I read and searched and waited… until I got to the very end, past the introduction, the methods, results, discussion, limitations, acknowledgement and the references.  I even used ‘word find’ for goodness sakes FIND: Sunlight or Sunshine.  Nada, nil, zilch.  Sunshine is not mentioned once in the study.

Below I offer a little information from the study, and then the email response from the corresponding author, because of course I emailed her.  I had to be doubly sure I didn’t overlook the part where the people talked about the time they spent in the sunlight.

Participants (54 people) agreed to wear a special light and activity sensor on their wrist (on the outside of their clothing) for 7 days.  This device generated data that the researchers could review, i.e., when the person fell asleep, how long they slept, when they were exposed to light – background, ambient light – and the level of intensity of that light.  The unit of measure for light is LUX.  The participants also completed a 7 day food intake diary and gave their heights and weights (for BMI calculation).  The goal was to see if timing and intensity of light was associated with sleep, eating, or BMI. 

The only finding that was considered ‘real’ was that people exposed to higher levels of light i.e., > 500 lux had lower BMI numbers than people not exposed to light above 500 lux.  This correlation only held if the exposure occurred in the early morning hours. 

It is probable that the light at > 500 lux was from the sun, but there is absolutely no way to confirm this.  Researcher Phyllis Zee kindly responded to my email inquiry and said that with a lux over 200 it is expected that sunlight was ‘involved,’ but the source of light was indeed unknown. Also, I think it is important to note that a BMI even if accurately representing excess adipose tissue is not something associated with the last 7 days!  One BMI point = 6 pounds and well, my BMI is about my last 7 years, not 7 days.

All that being said, Sunshine Makes Me Happy and that is all I need to know.

Reid, K. J., Santostasi, G., Baron, K.G., Wilson, J., Kang, J., & Zee, P. C. (2014). Timing and Intensity ofLight Correlate with Body Weight in Adults. PloS one, 9(4),e92251.