Although humans cannot produce energy from sunlight the way plants can, we do actually need sunlight to produce one essential nutrient, vitamin D.
The human body can also use vitamin D that it gets from its diet but like the sugars found in plants, the ultimate source of dietary vitamin D is also sunlight.
All vitamin D on planet Earth at one point was produced by a living creature in conjunction with sunlight. For example, fatty fish are high in vitamin D because they feed on other fish, which in turn fed on algae that produced their own vitamin D.
In recent years, scientists have discovered that mushrooms can also produce their own vitamin D. Because they tend to grow in dark conditions with minimal sunlight, the average culinary mushroom has only about 4 percent of the recommended daily allowance (RDA) for an adult human.
Yet, if mushrooms are artificially exposed to ultraviolet radiation, their vitamin D content can jump to 100 percent of the adult RDA! Some companies have also begun to sell mushrooms fortified in this way.