Vitamin D plays a key role in overall health, including immunity, sleep, bone maintenance, muscle growth, and brain function. It's also something our plugged-in, rarely-outside bodies commonly lack. Amp Human's D+ Lotion delivers a solid dose right through the skin. Just a pea-sized amount applied daily to the forearms can triple vitamin D levels in 3-4 months. Each application contains 5,000 IU, and each bottle holds a 60-day supply.