Your skin produces vitamin D when in direct sunlight, but you should not get your vitamin D from unprotected sun exposure or indoor tanning devices. Supplementing with vitamin D goes a long way towards inhibiting deficiency: we recommend about 125 mcg–200 mcg of vitamin D3 a day. If your multivitamin already delivers 25 mcg–75 mcg of vitamin D, Vitamin D3 125 mcg (5000 Iu) is perfect for achieving optimal vitamin D levels.