Most Americans don't have to contend with serious vitamin deficiencies, thankfully, but with an increasingly sedentary, indoor-dwelling population, fewer and fewer people get enough vitamin D. While it may not cause totally debilitating effects for everyone, a vitamin D deficiency can have some pretty serious consequences.
Why you need vitamin D
For kids, lack of what's known as the "sunshine vitamin" may result in rickets, which can bring along a whole bunch of fun stuff like bone deformities and fractures. While rickets in children is now rare in America, deficiency in vitamin D can cause a ton of issues even in adults, ranging from inflammation, a crappy immune system, osteoporosis, autoimmune disease, type 2 diabetes, as well as less-serious but still annoying symptoms like severe fatigue, hair loss, and an overall feelings of garbage-ness.
The Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies says that basically everyone who isn't a baby should take in at least 600 international units (IUs) -- unless you're over 70, then bump that up to 800 IUs. But no matter who you are, there's a good chance you're not getting enough.