The most important attack cells in the body’s immune system — T-cells that fight off infections — rely on vitamin D to do their jobs, Danish researchers reported this week in the journal Nature Immunology.

“The researchers found that immune systems’ killer cells, known as T cells, rely on vitamin D to become active and remain dormant and unaware of the possibility of threat from an infection or pathogen if vitamin D is lacking in the blood,” Reuters reported on Monday.

The news agency quoted Dr. Carsten Geisler of Copenhagen University’s department of international health, immunology and microbiology, who led the study: “When a T cell is exposed to a foreign pathogen, it extends a signaling device or ‘antenna’ known as a vitamin D receptor, with which it searches for vitamin D. This means the T cell must have vitamin D or activation of the cell will cease. If the T cells cannot find enough vitamin D in the blood, they won’t even begin to mobilize.”

This finding unlocks the mechanism behind what many vitamin D advocates have promoted for a long time: That the Sunshine Vitamin is key to proper immune health, and that natural levels of vitamin D are only indigenous in those who live and work outdoors, getting plenty of sunshine.

“Most Vitamin D is made by the body as a natural by-product of the skin’s exposure to sunlight. It can also be found in fish liver oil, eggs and fatty fish such as salmon, herring and mackerel, or taken as a supplement,” Reuters reported, acknowledging what Sunshine Vitamin advocates understand, “Almost half of the world’s population has lower than optimal levels of vitamin D and scientists say the problem is getting worse as people spend more time indoors.”

To read the Reuters report click here.