Norwich scientists have boosted the amount of vitamin D in tomatoes by altering the plants' genetic code.

Researchers at the John Innes Centre (JIC) said the breakthrough offers a "sustainable solution" to a global health problem - as millions of people are estimated to be deficient in vitamin D, needed for healthy bones and muscles.

It is also know as the "sunshine vitamin" as it is produced in the human body from sunlight absorbed by the skin.

But in winter, and in higher latitudes, many people need extra vitamin D from supplements or from a small number of foods including oily fish, red meat and egg yolks.

Plants are generally poor sources, and while tomato leaves naturally contain very low levels of one of the building blocks of vitamin D, called provitamin D3, it is not normally found in ripe tomatoes.

But scientists used new "gene editing" techniques to "switch off" a particular plant enzyme to allow provitamin D3 to accumulate in the fruit. This was then converted to vitamin D3 through exposure to ultraviolet (UVB) light.

The JIC team said one edited tomato contained the same levels of vitamin D as two medium-sized eggs or 28g of tuna.

The study, published in the Nature Plants journal, says the leaves also contained much higher high levels of provitamin D3, so these usually-wasted parts of the plant could be used for the manufacture of vegan-friendly vitamin D3 supplements or food fortification.

Dr Jie Li, first author of the study, said: “The Covid-19 pandemic has helped to highlight the issue of vitamin D insufficiency and its impact on our immune function and general health.

"The provitamin D enriched tomatoes we have produced offer a much-needed plant-based source of the sunshine vitamin.

"That is great news for people adopting a plant-rich, vegetarian or vegan diet, and for the growing number of people worldwide suffering from the problem of vitamin D insufficiency.”

Gene editing is different to the controversial process of genetic modification (GM), as scientists can target and manipulate specific genes already present in an organism, rather than introducing DNA from different species.

Later this week, the government is expected to introduce a bill aiming to speed up production of crops edited to be more resistant to disease and drought, and less reliant on chemical fertilisers, in a bid to improve British food security in the wake of the war in Ukraine.