Dietary supplements may upset the balance in the body's cells and therefore cause more harm than good, according to new research from Norway.
The study, which is being conducted by a research group at the Biotechnology Centre at the University of Oslo, has found that the body's responses to stress are important in preventing DNA from eroding.
"I fear that the fragile balance in our cells can be upset when we supplement our diet with vitamin pills," said Hilde Nilsen, head of the research group.
Maintenance of genes
The body's DNA — the genetic code that makes a person who they are — is constantly exposed to damage. In each of the hundred trillion cells in the body, up to two hundred thousand instances of damage to the DNA take place every day. These may stem from environmental causes such as smoking, stress, environmental pathogens or UV radiation. But the natural and life-sustaining processes in the organism are the primary sources of damage to the DNA.
Small worm shows "repair" genes
The researchers used a small organism — a one millimetre long nematode called Caenorhabditis elegans (C. elegans) — to examine how damage to DNA might be repaired in order to live a healthy and long life. The roundworm, which lives for only 25 days, has 20,000 genes, only a few thousand fewer than humans.
"C. elegans is a fantastically powerful tool, because we can change its hereditary properties," Ms Hilde said. "We can increase its ability to repair DNA damage, or we can remove it altogether. We can also monitor what happens when damage to DNA is not repaired — in several hundred specimens and through their entire lifespan," she said.
Different "repair proteins" take care of various types of damage to the DNA. The most common ones are repaired by 'cutting out' and replacing a single damaged base — by itself or as part of a larger fragment.
'Underactive' genetic control affects lifespan
In some specimens of the worm that did not have the ability to repair the damage, the researchers observed that the ageing process proceeded faster than normal. It has been thought that the ageing process occurs because damage accumulates in the DNA and prevents the cells from producing the proteins they need for their normal operation, but the University of Oslo researchers said this might not actually be the case.
One of the genes studied by the researchers has a somewhat shortened lifespan: on average, this mutant gene lived three days less than usual. Translated into human terms, this would mean dying at the age of 60 rather than 70.
"We were surprised when we saw that these mutants do not in fact accumulate the DNA damage that would cause ageing," Ms Hilde said. "On the contrary: they have less DNA damage.
This happens because the little nematode changes its metabolism into low gear and released its own antioxidant defences," she said.
"Nature uses this strategy to minimise the negative consequences of its inability to repair the DNA," Ms Hilde said. "So why is this not the normal state? Most likely because it comes at a cost: these organisms have less ability to respond to further stress — they are quite fragile," she said.
The researchers said they had shown for the first time that this response was "underactive genetic control" and was not caused by passive accumulation of damage to the DNA, as has been widely believed. They said that further research showed that other repair proteins were responsible for inhibiting damage that they failed to repair completely.
"The consequence is that they establish a barrier — a road block," Ms Hilde said. "This triggers a cascade of signals that reprogram the cell," she said.
Researchers said it was important to remember that the purpose of DNA repairs was most likely to "ensure that we produce healthy offspring — not necessarily that we live as long as possible after our reproductive age interval".
"Initiating a survival response that reinforces the antioxidant defences means that a lack of ability to repair the DNA has less impact that it would otherwise have on our reproduction," Ms Hilde said. "To the species as a whole, it's a small cost that some individuals will be less good at handling stress and have a shorter life," she said.
Because this is an active process within the cells, the researchers referred to it as reprogramming.
"We have found several proteins that trigger this reprogramming," Ms Hilde said. "The process has the same effect as a reduction in caloric intake, which we know helps increase the lifespan in many species. In other words, there are two routes to a long life. When we stimulate both of these two routes in our nematode at the same time, we can quadruple its normal lifespan," she said.
Synthetic antioxidants could upset body's balance
Researchers said the balance between oxidants and antioxidants was crucial to human physiology, but exactly where this equilibrium lies varies from one person to the next.
"This is where I start worrying about the synthetic antioxidants," Ms Hilde said. "The cells in our body use this fragile balance to establish the best possible conditions for themselves, and it is specially adapted for each of us. When we take supplements of antioxidants, such as C and E vitamins, we may upset this balance," she said.
The researchers said that while it sounded "intuitively correct" that intake of a substance that may prevent accumulation of damage would benefit a person, the research indicated that supplementing diet with vitamins may "cause a lot of harm".
"The health authorities recommend that instead we should seek to have an appropriate diet," Ms Hilde said. "I'm all in favour of that. It's safer for us to take our vitamins through the food we eat, rather than through pills," she said.
