Study: Exposure To Morning Sunlight Helps Managing Weight 137
jones_supa (887896) writes "A new Northwestern Medicine study reports the timing, intensity and duration of your light exposure during the day is linked to your weight — the first time this has been shown. People who had most of their daily exposure to even moderately bright light in the morning had a significantly lower body mass index (BMI) than those who had most of their light exposure later in the day, the study found. It accounted for about 20 percent of a person's BMI and was independent of an individual's physical activity level, caloric intake, sleep timing, age or season. About 20 to 30 minutes of morning light is enough to affect BMI. The senior author Phyllis C. Zee rationalizes this by saying that light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance. The study was small and short. It included 54 participants (26 males, 28 females), an average age of 30. They wore a wrist actigraphy monitor that measured their light exposure and sleep parameters for seven days in normal-living conditions. Their caloric intake was determined from seven days of food logs. The study was published April 2 in the journal PLOS ONE. Giovanni Santostasi, a research fellow in neurology at Feinberg, is a co-lead author."
Re:correlation does not prove causation (Score:4, Insightful)
In any case causation is not proven, and this is a pretty small sample anyway.
worth more research (Score:4, Insightful)
as the summary points out, it was only for 7 days with 54 people who used wrist mounted light sensors & 'food logs' but it's definitely worth a look
sunlight in the morning has all kinds of physiological benefits...IIRC recently it was linked to higher immune function
Re:Vitamin D (Score:2, Insightful)
Is this caused by Vitamin D perhaps? It would be interesting to compare to people on supplements.
Here in Edmonton, Canada, my family Dr. was participating in a study where her patients were tested to Vitamin D. I ended up having to take 2000 IU a day. Not that I don't get outside; during about six months of the year you won't see any daylight from 5 pm to 9 am.
I highly doubt it, even if it were because of Vitamin D, people on placebos, erm sorry, supplements wouldn't get the same effect.
However I think the cause it more due to the notion that if people are outside... they're moving instead of sitting down so they're burning more calories.
Re:Statistically Insignificant (Score:2, Insightful)
For seven days. Either dredging the data from something else or (worse) looking for the effect!. Which is claimed to be 20% of BMI. I can refute this trivially within my own household. This is arrant nonsense. For me dropping 20% of BMI means losing 40 pounds, and gee, I'll bet nobody in their study dropped 40 pounds in seven days. So precisely how could the establish the correlation? By enrolling a handful of thin early risers and fat late sleepers and watching them for seven days and concluding that the relevant controlling variable was the brightness of the light they were exposed to when they got up?
Sometimes one doesn't even have to RTFA to sneeze out a "bullshit" and move on.
rgb
Re:correlation does not prove causation (Score:5, Insightful)
If they really wanted to find out whether sunlight affected weight, they would have done a randomized, controlled trial.
They would have randomly assigned half the people to getting exposed to sunlight early, and the other half to getting exposed to sunlight late.
Instead, they let the subjects go their merry way and simply measured their exposure to sunlight during the day.
These kind of studies give spurious results. For example, suppose the ones who are exposed to sunlight in the morning are getting up early to start their day jogging.
Re:correlation does not prove causation (Score:5, Insightful)
If they really wanted to find out whether sunlight affected weight, they would have done a randomized, controlled trial.
They would have randomly assigned half the people to getting exposed to sunlight early, and the other half to getting exposed to sunlight late.
Instead, they let the subjects go their merry way and simply measured their exposure to sunlight during the day.
These kind of studies give spurious results. For example, suppose the ones who are exposed to sunlight in the morning are getting up early to start their day jogging.
Well, no.
You don't begin a line of inquiry with a randomized, controlled trial. You begin with a study to see if there may be a correlation.
Why? If there's no correlation in a study, then there's no reason to spend the (much greater) money on a randomized trial.
If there does appear to be a correlation, you report it so that you (and others) may pursue the inquiry further.