Healthy reasons to pull down the shades

Satellite pictures reveal that big chunks of planet Earth are lit up like a Christmas tree at night. It's a breathtaking sight. But here are three great reasons to impose your own blackout at bedtime:

1. DIM YOUR OBESITY RISK. Light at night (all except red light waves) seems to disrupt your body's internal dinner bell, making it ring "time to eat" at the wrong times, and also prodding you to eat more.

2. AVOID A HIDDEN DEPRESSION TRIGGER. Whether it's the glare of a streetlight or the glow of a computer screen, having lights on while you're sleeping can reduce connections between your brain cells. You won't just forget who won last year's Super Bowl (the Saints) or last season's "Dancing With the Stars" (Jennifer Grey), new research shows that you're also at greater risk for depression.

3. SWITCH OFF A CANCER PROMOTER. The reason isn't clear yet, but the connection is sure there: Several studies show that light exposure at night (whether you work the late shift or during sleep) increases your risk for some cancers. Light exposure at night may encourage tumor growth. And prostate cancer rates are higher in countries with the most nighttime illumination.

What's going on? Light (except red light waves) seems to reduce levels of melatonin, a hormone that helps ensure a restorative night's sleep and suppresses cancer growth. So, do what it takes - pull down the shades, close the curtains and/or use a sleep mask (especially if you're a night-shift worker) - to get your nightly quotient of darkness.