Teenagers have this delightful tendency to favour the indoors -- you know, that whole sleeping all day, emerging only to talk on the phone, text friends or read celebrity gossip. Oh wait, that kind of sounds like my life. Ah, the life of a freelancer.

Anyway, teenage girls have a very good reason to venture outdoors on a regular basis because a new study shows that a lack of vitamin D (provided by the sun's rays) can stunt an adolescent girl's growth and -- worse yet, if you ask them -- cause weight gain. You can get vitamin D in supplement form, but why bother when you can get the same results from a few minutes of outdoor time every day.

That doesn't mean that you're off the hook if you're well past puberty. A lack of vitamin D in adults is even more serious, potentially leading to osteoporosis, cancer and other deadly diseases.