Vitamin D, the sunshine vitamin, seems to be the nature's best antibiotic, for a new study says that it fends off infections by boosting the immune system.

Researchers in Denmark have found that vitamin D, which can be obtained from food or manufactured by human skin exposed to the sun, triggers and arms the body's T-cells which seek out and destroy any invading bacteria and viruses.

According to them, vitamin D is crucial to activating human immune defences and that without its sufficient intake, the killer cells of the immune system -- T-cells -- willn't be able to react to and fight off serious infections in the body.

For T-cells to detect and kill foreign pathogens such as clumps of bacteria or viruses, the cells must first be "triggered" into action and "transform" from inactive and harmless immune cells into killer cells that are primed to seek out and destroy all traces of invaders.

The researchers found that the T-cells rely on vitamin D in order activate and they would remain dormant, "naive" to the possibility of threat if it is lacking in the blood.

Lead researcher Professor Carsten Geisler of Copenhagen University was quoted by 'The Daily Telegraph' as saying, "When a T-cell is exposed to a foreign pathogen, it extends a signalling device or 'antenna' known as a vitamin D receptor, with which it searches for vitamin D.

"This means that 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 mobilise.”