By making a few genetic tweaks using CRISPR technology, scientists have designed a special sun-dried tomato packed to the leaves with vitamin D.

The flesh and peel of the fruit were genetically engineered to contain the same vitamin D levels as two eggs or 28 grams of tuna, both of which are currently recommended sources of the vital nutrient.

When exposed to ultraviolet light for an hour, these provitamins were readily converted to vitamin D3.

Both the provitamin and the vitamin come with potential health-related benefits.

"We've shown that you can biofortify tomatoes with provitamin D3 using gene editing, which means tomatoes could be developed as a plant-based, sustainable source of vitamin D3," says botanist Cathie Martin who works at The John Innes Center, an independent center for plant research in England.

"Forty percent of Europeans have vitamin D insufficiency and so do one billion people world-wide. We are not only addressing a huge health problem, but are helping producers, because tomato leaves which currently go to waste, could be used to make supplements from the gene-edited lines."

Among the gene-edited tomatoes, researchers found the edible green leaves contained 600 micrograms of provitamin D3 per gram.

That's 60 times greater than the recommended daily intake for adults.

The authors aren't suggesting people eat tomato leaves along with the flesh, but rather that the we use the greenery instead of throwing away. For instance, the leftover leaves could be ground down to make vegan-friendly vitamin D3 supplements.

If we're smart about this, it seems every part of the genetically engineered fruit can be used to tackle vitamin D deficiency.

While exposure to the sun is one way to boost vitamin D levels in the human body, diet is another major source. That said, there are very few foods that naturally contain the vitamin and even fewer that are vegan.

As a result, products like milk, cereal, and orange juice have been artificially fortified with vitamin D to help boost public health.

Tomatoes, however, naturally contain some precursors to vitamin D3, known as 7-dehydrocholesterol, or 7-DHC.

By turning off the genes that encode for enzymes that break down 7-DHC, researchers forced the vitamin D precursor to accumulate in both unripe and ripe fruit.

This precursor can then be readily converted to vitamin D in the presence of sunlight, but it doesn't necessarily have to be to show benefits.

"For the elderly with declining levels of 7-DHC, consuming fruit biofortified with 7-DHC might address their deficiencies directly," the authors write.

Even better, the genetic tweaking caused no changes to tomato growth, development, or yield.

Given that vitamin D deficiency is linked to an increased risk of cancer, Parkinson's disease, depression, and dementia, biofortifying fruits and vegetables with the nutrient could possibly go a long way towards improving public health.

In light of the promising results, researchers are calling for tomatoes to be the next plant-based, sustainable source of vitamin D3. And they might not be the last, either.

Eggplants, potatoes, and peppers all have similar precursors to vitamin D3 that could be tweaked in similar ways to accumulate in the plants.

"The provitamin D enriched tomatoes we have produced offer a much-needed plant-based source of the sunshine vitamin," says plant scientist Jie Li, who works in Martin's lab as a postdoctoral researcher.

"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."

The study was published in Nature Plants.