If British scientists have their way, two medium-sized tomatoes a day could keep the doctor away.

A research team led by scientists at the John Innes Centre in Norwich, in the east of England, have edited the genetic makeup of tomatoes to become a robust source of vitamin D, which regulates nutrients like calcium that are imperative to keeping bones, teeth and muscles healthy.

Although vitamin D is created in our bodies after exposure to sunlight, its major source is food - largely dairy and meat, which can cause a challenge to vegetarians and vegans.

Low vitamin D levels - associated with conditions from cancer to cardiovascular disease - affect roughly a billion people globally, the researchers said.

Tomato leaves naturally contain one of the building blocks of vitamin D3, called 7-DHC. Vitamin D3 is considered best at raising vitamin D levels in the body.

The scientists used the Crispr tool, designed to work like a pair of genetic scissors, to tweak the plant's genome so 7-DHC accumulates in the tomato fruit, as well as the leaves.

When leaves and the sliced fruit were exposed to ultraviolet light for an hour, one tomato contained equivalent levels of vitamin D as two medium-sized eggs or 28 grams of tuna, the researchers wrote in a paper published in the journal Nature Plants.

Most vitamin D3 supplements come from lanolin, which is extracted from sheep's wool. Since the sheep stays alive, it works for vegetarians, but not vegans.

The scientists are now evaluating whether sunshine, instead of ultraviolet light, can effectively convert 7-DHC to vitamin D3.

To close the current gap in the intake of vitamin D from dietary sources, two medium sized gene-edited tomatoes should be enough, said the study's lead author, Jie Li, adding it is hard to tell a gene-edited tomato apart from a wild tomato.

"They taste like tomatoes," added Cathie Martin, another study author.