There's been much speculation about whether vitamin D might prevent or help survival with COVID-19, and two new studies appear to underscore the link. In the first study -- published in the journal Aging Clinical and Experimental Research -- British researchers found that COVID-19 infections and deaths were higher in countries where people had low vitamin D levels, such as Italy and Spain, compared to northern European countries where average vitamin D levels were higher. The researchers explained that people in southern Europe may have darker pigmentation, which reduces vitamin D synthesis, while people in northern European countries consume more cod liver oil and vitamin D supplements. The second study appeared in the online journal medRxiv, but has not been peer-reviewed. In it, a team from Northwestern University in Evanston, Ill., analyzed data from 10 countries, including the United States. Led by postdoctoral researcher Ali Daneshkhah, the study's conclusion was the same: Low vitamin D levels were linked to a hyperactive immune system. The so-called "sunshine vitamin" bolsters immunity and prevents an overactive immune response, the Northwestern researchers said, adding that their finding could explain several mysteries, including why kids are unlikely to die from COVID-19.