For centuries, mothers have wrongly told their children that eating carrots will improve their vision. The sight-enhancing properties of these iconic vegetables is be a myth (albeit a fascinating one involving Nazis and fighter pilots) but if Jay Morris has anything to say about it, they may soon be better known for building strong bones.
Morris, together with Kendal Hirschi and other Texan colleagues, has found a way to double the calcium content of carrots through genetic modification, making them a rich source of the element that is so vital for bones
The team loaded their super-carrots with a protein called sCAX1, which pumps calcium into the plant’s cells. The protein originally hailed from the plant-of-choice for geneticists, Arabidopsis thaliana, where it exists in a larger version. Morris’s team lopped off a small piece from its tip that stops the protein from funnelling in more calcium once a certain amount has been reached.
In this shortened form, sCAX1 is relentless in its import of calcium and the researchers have found that it can greatly increase the calcium content of several vegetables including tomatoes, potatoes and carrots. These super-charged vegetables could help to reduce the risk of osteoporosis, one of the world’s leading nutritional disorders, where a lack of calcium leads to brittle bones.
In general, vegetables, fruits and other plant-based foods are being increasingly pushed by health organisations as a way of stemming the rising global levels of obesity as well as reducing the rates of several chronic diseases. But vegetarian menus aren’t the final word in nutrition; vegetables are certainly loaded with nutrients but compared to a carnivorous menu, vegetarian ones lack certain key nutrients, including calcium.
One solution is to artificially boost the levels of missing nutrients in these foods. Morris’s team proved that this is feasible by growing their altered sCAX1 carrots and running them through animal and human trials.
They grew the carrots using hydroponics; rather than soil, they were ‘planted’ in a solution containing important minerals. This nutrient bath included a very mildly radioactive isotope of calcium that was taken up by the carrots and acted as a label for their calcium content. It revealed that the edible parts of the super-carrots had twice the amount of calcium of normal ones.
The researchers then fed the labelled carrots to mice. Sure enough, the rodents managed to build up the same amount of calcium by eating half the amount of sCAX1 carrots as normal carrots.
Human trials were also successful, but to a lesser extent. Thirty volunteers munched on the enhanced carrots, this time labelled with a different non-radioactive isotope of calcium. Morris measured this isotope in urine samples, marking the first time that such labels have been used to reveal the true nutritional value of genetically modified foods. Pound for pound, the diet of super-carrots provided people with 42% more calcium than the regular varieties.
Benefits and risks
Morris’s tinkered carrots are not only more nutritious but also more long-lasting and more productive. Again, calcium is the key. Farmers have known this for some time. Many growers soak apples in calcium solutions to keep them firm during shipping and fresh on the shelf. Potato crops are also sprayed with extra calcium, which helps them to tolerate hot conditions and ward off infections. There’s good reason to believe that the modified carrots would also enjoy similar benefits.
Morris is clear that the carrots are not the sole answer to calcium deficiencies. Enriched though they are, they can only provide a small proportion of a person’s calcium intake. But Morris argues that the technique is readily transferable to other vegetables. The key will be to increase calcium levels across a whole range of food.
Some might decry the need for such biological tinkering at all. After all, calcium supplements are already widely available. Even so, Morris argues that science is generally finding that these supplements are far less beneficial to health than nutrients obtained directly from our diets. In some cases, they could even be harmful.
It might also be worth noting that the carrot has already been driven away from its natural state. In its original Central Asian form, it is a purple or yellow vegetable. The familiar orange hue is a Dutch invention form the 15th or 16th century, when the colour symbolised the ruling House of Orange and appealed to patriotic growers.
History aside, it is encouraging that Morris is taking the safety of the super-carrot seriously. His paper ends on a cautious note. The main concern for the moment is that sCAX1 is not a one-trick protein. As well as calcium, it will also absorb other similarly charged metal ions including zinc, which is good, and cadmium, which is not.
Cadmium is a potent carcinogen and it would be a bad move to breed vegetables that soak up and store large amounts from the surrounding soil. In Morris’s experiments, the sCAX1 carrots were grown in hydroponic solutions that were free of any cadmium. What would happen in real farming conditions is a matter for another experiment.
Reference: Morris, J., Hawthorne, K.M., Hotze, T., Abrams, S.A., Hirschi, K.D. (2008). Nutritional impact of elevated calcium transport activity in carrots. Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0709005105