How many times did your parents make you go outside and play? You should call and thank them.

That’s because you likely absorbed much-needed vitamin D, which might be why you’re such a happy person today.

The most natural way to get vitamin D is by exposing your bare skin to sunlight (ultraviolet B rays). This can happen very quickly, particularly in the summer.

Why does this matter? Your body need vitamin D to absorb calcium and make your bones stronger, WebMD reports.

You can also get vitamin D by taking supplements, although research from the United Kingdom suggests few children's multivitamins actually offer the recommended daily dose of vitamin D.

» Nutrients from food, not supplements, will help you live longer, study says

A new study suggests vitamin D might also might lead to aggressive behavior in adolescents.

University of Michigan researchers say they have found a link between vitamin D deficiency in young kids and aggression in adolescents. According to their study of schoolchildren in Bogotá, Columbia, almost young kids with low levels of the vitamin were nearly twice as likely to exhibit aggression as they got older.

"Children who have vitamin D deficiency during their elementary school years appear to have higher scores on tests that measure behavior problems when they reach adolescence," said Eduardo Villamor, professor of epidemiology at the U-M School of Public Health and senior author of the study appearing in the Journal of Nutrition.

» Are child multivitamins misleading? Scientists concerned about vitamin D dosage

Villamor said vitamin D deficiency also has been associated with depression and schizophrenia in adulthood.

The researchers admit their study has limitations, but believe their results "indicate the need for additional studies involving neurobehavioral outcomes in other populations where vitamin D deficiency may be a public health problem."

» Vast majority of vitamins do not improve health, study says