A lack of vitamin D has been discovered in 80% of people suffering from Covid-19.
Research shows low levels of the vitamin in many people who have tested positive.
Vitamin D is known to help the immune system fight off infections like colds and flu.
It is made in the body’s kidneys, but extra dosages come from being out and about in the sunshine.
It can also be found in fish, red meat, egg yolks and fortified cereals.
About 20% of Britain’s population have low vitamin D levels.
The report’s co-author Dr Jos Hernandez, of the University of Cantabria in Spain, said:
“Vitamin D treatment should be recommended in COVID-19 patients with low levels of vitamin D circulating in the blood
“This approach might have beneficial effects in both the musculoskeletal and the immune system.
“Vitamin D deficiency has been linked to a variety of health concerns, although research is still underway into why the hormone impacts other systems of the body.
“Many studies point to the beneficial effect of vitamin D on the immune system, especially regarding protection against infections.”
The findings were published in the Journal of Clinical Endocrinology & Metabolism.