Washington, Nov 4 (IANS) A must for good health, vitamin D also needs activation to function optimally within the human body. Until recently, this activation was thought to happen in the kidneys, but a new University of Iowa study has found that the activation can also take place in lung airway cells.

The study also links vitamin D produced in airway cells to activation of two genes that help fight infection.

Besides helping absorb calcium absorption, vital to bone health, vitamin D is increasingly recognised for its beneficial effects on the immune system.

Its deficiency has been recently linked to increased risk of some infections, autoimmune diseases such as multiple sclerosis and type-1 diabetes, and some cancers.

“The more scientists have been studying vitamin D, the more we learn about new roles it plays in the human body,” said the study’s co-author Sif Hansdottir, fellow in internal medicine at the University of Iowa (U-I) Carver College of Medicine.

“The active form of vitamin D is known to affect the expression of more than 200 genes, so we were interested both in the possible lung-specific production of active vitamin D and in vitamin D-dependent production of proteins that fight infections.”

The first step in vitamin D activation takes place in the liver, where an enzyme called 25-hydroxylase converts vitamin D into a “storage” form.

The next step takes place typically in the kidneys, but in recent years, tissue and organs such as skin, intestines, breast and prostate have been found also to express the enzyme that completes vitamin D conversion, said an U-I press release.

“When we put the storage form of vitamin D on the lung airway cells, we saw them convert it to the active form,” Hansdottir said. “The next step was to investigate whether this active form could affect the expression of genes.”

The team then showed that vitamin D activated by airway cells affects two genes involved in immune defence. One gene expresses a protein called cathelicidin that can kill bacteria. The second gene, called CD14, produces a protein that helps cells recognise different kinds of pathogens that could be a threat.

“Vitamin D not only increases proteins involved in bacterial killing but also can dampen inflammation,” Hansdottir said.

American Academy of Paediatrics recently recommended that vitamin D dosage for children be increased to 400 IU (international units) per day. Optimal daily intake for adults is still being studied but may be as high as 800 to 1,000 IU.

The results will appear in the Nov 15 issue of the Journal of Immunology.