Are you vitamin D deficient? Odds are, someone in your family is. A recent study of over 70,000 participants found that one in four either had a moderate or severe vitamin D deficiency. That’s not all: 40% had a mere insufficiency – which is less to worry about than a deficiency, but still not ideal. Put together, that makes well over half of Americans projected to lack sufficient vitamin D. But how would you know? The “super supplement” may be the only one worth taking, scientists say. But before you empty your piggy bank on the drugstore counter, you’d best brush up on the essential signs yo…