|Golden rice and white rice. Photo By International Rice Research Institute (IRRI) [CC-BY-2.0 |
(http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
Every so often, a little bit of new science shines a spotlight on the danger of trying a simplistic, GM quick-fix to address a complex problem.
Golden rice first hit the headline decades go. The carrot-tinted rice is genetically transformed to generate beta-carotene, which our bodies convert to vitamin A. It's aimed at supplementing the diet of vitamin-A deficient populations in developing countries whose staple diet is rice and little else.
Vitamin-A is critical to human vision, bone and skin health, metabolism and immune function. It's involved in the direct activation of several hundred genes. In the mammalian embryo (including human), this global effect on genes renders the vitamin essential for development, growth and tissue differentiation. Chronic deficiency of vitamin-A can be catastrophic.
But, the golden rice has still not made it out there. And, perhaps this is just as well, because beta-carotene has, it seems, a dark side.
While attention to dietary provision of vitamin A is a priority, science has now shown that equal attention must be paid to over-provision.
New research has revealed that beta-carotene is broken down in plants and animals to form a host of biologically active derivatives which can circulate in the body: only one of these is vitamin-A. While some of these by-products promote the activity of the vitamin form, other inhibit it. The concern is that unnaturally elevated levels of beta-carotene in a food will generate unnaturally elevated levels of the inhibitory derivatives and result in vitamin-A suppression. On a diet dependent on beta-carotene-fortified GM rice, the over-fed could end up with the same vitamin deficiency diseases as the underfed.
Previously puzzling science which found that beta-carotene actually promoted the cancer it was expected to prevent can now be explained. The CARET study sought to show that beta-carotene supplements would protect smokers and asbestos workers against lung-cancer. It sent shock-waves through the scientific community when the trial had to be prematurely halted because the supplemented subjects were exhibiting a higher incidence of disease. It now seems likely that the oxidative stress from smoke inhalation was interacting with the 'protective' beta-carotene supplement to generate an excess of the derivatives which inhibit vitamin-A
The moral of this tale is don't smoke, don't eat golden rice, and never do both at once.
Also remember that Roundup herbicide, accumulated by glyphosate-tolerant GM crops, also interferes with the vital action of vitamin-A in the embryo (see ROUNDUP CAUSES BIRTH DEFECTS - GMFS News archive, October 2010). Who knows what Roundup plus excess beta-carotene might do.
Nature doesn't do simple cause-and-effect mechanisms like the biotech industry. Nature does interlocking systems of fine balances which can be upset only too easily by the clumsy human hand.
Worryingly, this example of a vitamin with its own natural retinue of helpers-hinderers may well be a model for the way in which many other such essential nutrients operate in the body.
Second-generation GM foods full of 'healthy' GM oils and 'disease-busting' GM anti-oxidants may be with us soon: don't be fooled into believing that any unnaturally generated substances will be good for you.
- Abjulkerim Eroglu et al., 2012, Naturally Occurring Eccentric Cleavage Products of Provitamin A β-Carotene Function as 'Antagonists of Retinoic Acid Receptors, Journal of Biological Chemistry, 287:19
- Nathan Gray, Researchers reveal 'dark side' to high beta-carotene intake, www.nutraingredients.com, 3.05.12