The Download: the secrets of vitamin D, and an AI party in Africa

Plus: Google's new image generator has extremely loose guardrails We're learning more about what vitamin D does to our bodies At a checkup a few years ago, a doctor told me I was deficient in vitamin D. But he wouldn't write me a prescription for supplements, simply because, as he put it, everyone in the UK is deficient. Putting the entire population on vitamin D supplements would be too expensive for the country's national health service, he told me. But supplementation--whether covered by a health-care provider or not--can be important. As those of us living in the Northern Hemisphere spend fewer of our waking hours in sunlight, let's consider the importance of vitamin D. Read the full story . This article first appeared in The Checkup, MIT Technology Review's weekly biotech newsletter. Here's why we don't have a cold vaccine.