For most of history, humans got all the Vitamin D they needed simply by being outdoors, absorbing the sun’s ultraviolet light. Ultraviolet radiation triggers the body’s production (a two-step process involving both liver and kidney) of the vitamin, which is technically a hormone. What the body didn’t use right away, it stored in fat.

But over the millennia, humans moved into the shade. They migrated from equatorial regions to less sunny latitudes, switched from hunting and farming to indoor jobs and — just in the past few decades — began slathering themselves with sunscreen.

As scientists in recent years began to assess the extent and import of this diminished exposure to sunlight, they’ve also amassed compelling research showing just how vital Vitamin D may be.

Identified in the early 20th Century as the best defense against the bone-softening disease rickets, Vitamin D has since been lauded for fending off osteoporosis and hip fractures in older people (by empowering calcium to strengthen bones and probably by boosting muscle strength, which helps keep people on their feet). Some research even suggests Vitamin D may work in the brain to improve balance, another boon to tumble-prone seniors.

Researchers have discovered that nearly every kind of tissue in the body is equipped with Vitamin D receptors, which suggests that the substance may be involved in all kinds of functions.

Though studies of Vitamin D’s role in cancer prevention have not proved conclusive, it appears likely that the vitamin may help protect against colon cancer and perhaps against breast and prostate cancer.

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