Ridley: A gene-edited tomato could end our vitamin D crisis

A few years ago a routine blood test told me that I, like much of the British population, suffered from vitamin D deficiency. Around 18 per cent of Britons are deficient year-round, rising to 31 per cent in winter.

Sunlight makes vitamin D in our tissues in summer, but the lack of it in winter leaves us scrabbling to get enough of the stuff from eggs, fish and meat. Deficiency can cause rickets in children and affect the immune system, leaving people more vulnerable to respiratory infections in particular.

So news of the development of a tomato rich in vitamin D—at the John Innes Centre in Norwich—is very welcome. If trials go well, it will be one of the first products of precision breeding by gene editing: a technology that promises a rich harvest of improvements in plants.

But perhaps more important, it represents a switch from breeding plants that benefit the farmer to ones that benefit the consumer. One reason people have resisted the genetic engineering of food plants is the perception that the scientists seemed mostly to be helping the producers—by improving yields or resisting insect pests—and offering nothing to us mortals who eat the stuff.

Now, with gene editing, some of the work of plant breeders is focused on redressing that balance and making food naturally healthier.

In this case, the “sunshine” tomato directly addresses a vital medical need. Indeed, such has been the impact of the dearth of vitamin D in human history that extremely fair skin and blue eyes probably evolved in northern Europe around 5,000 years ago specifically to combat this deficiency.

Hunter-gatherers were mostly able to maintain healthy levels of the vitamin from fish and meat, but the invention of cereal farming—and its penetration much farther north in Europe than elsewhere on the planet—would have left the people who lived around the North Sea exposed to chronic deficiency in winter.

As one of the cloudiest countries in the world, Britain is especially at risk of vitamin D deficiency. The elderly, the obese, people who spend most of their lives indoors and those with darker skins are most prone to the deficiency.

All of those categories are steadily growing as proportions of the population, yet the NHS’s interest in the problem seems to have faded somewhat in recent years. Only general advice (rather than direct provision) to take supplements has been issued, and rather quietly.

Indeed, the NHS discourages widespread testing for vitamin D lest it lead to people overdosing themselves or rewarding the supplements industry. My reading of the evidence suggests that most supplements are probably a waste of time and money for most people—apart from vitamin D, omega-3 acids and perhaps turmeric.

During the COVID pandemic, David Davis MP and I tried to push the government to distribute vitamin D supplements, knowing from studies that a deficiency in this substance can worsen the impact of respiratory infections.

I was told by one professor that it was not a silver bullet to ending the pandemic. I told him I knew that, but stressed it could make all the difference at the margin when it came to how sick a vulnerable person became.

Epidemiological studies did indeed find “an inverse correlation between vitamin D deficiency and an increased risk of severe disease, hospitalization, and mortality in COVID-19 patients,” though supplements taken after infection did not appear to have an effect.

Rather than treating vitamin D deficiency as a medical issue (children in particular hate taking pills), the best approach may be to see it as a nutritional one.

Prof Cathie Martin of the John Innes Centre discovered that tomatoes could be made to accumulate a precursor of vitamin D by deleting a 108-letter sequence in a particular gene. No new DNA was added, just a simple editing alteration of the kind that could have happened naturally.

The Quadram Institute has fed tomato soup made with the new variety to volunteers in Norwich to test whether they do indeed boost vitamin levels compared with controls eating normal tomato soup.

Preliminary results reported at the American Nutrition Society Meeting in July were very encouraging. Tomatoes are used in many cooked products, so they could smuggle the vitamin into people’s diets painlessly and freely.

“If I can encourage people to eat more tomatoes not only for their vitamin D3 content but also for all the other vitamins (A, B1-B9, C, E and K) and their fibre I would be content,” Prof Martin tells me.

Prof Martin and others learnt the hard way from the genetically modified purple tomato that took 17 years to reach the market in America, Canada and Australia (but not here) that new products need to look and taste great so that consumers will freely choose them.

So the new precision-bred “sunshine” tomato, produced by means indistinguishable from natural evolution, should soon be adorning our pizzas—but not those of citizens of the European Union, which remains stubbornly resistant even to this technology.