Good news for sun-lovers (aka everyone): Vitamin D is essential for bone strength and increases collagen production. This which means less wrinkles and younger-looking skin. Another positive reason to keep your levels high? Getting too little sunlight, and therefore, having low D levels, has been associated with depression. And new research from University of Georgia found a strong link between D deficiency and seasonal affective disorder (SAD) a type of seasonal depression that occurs in the winter when sunlight is at a minimum and the sky tends to be dark and gloomy— causing your mood to follow suit. Vitamin D3 is important for producing feel-good chemicals serotonin and dopamine in the brain. Low levels of both are linked to depression, making a strong case for vitamin D’s role in helping regulate mood.