Ever since the free radical theory of aging was conceived in the 1950s, antioxidants have been a buzz word in health - saturating the cosmetic industry and contributing to a smoothie blending, supplement popping boom. While antioxidants can certainly play an essential role in health, there is growing evidence that additional supplementation has limited benefit and can actually be harmful in some cases.
Aging has yet to be ascribed to one, singular cause and the free radical theory has struggled to prove itself. While in some organisms reducing oxidative stress can prove beneficial and increasing mitochondria targeted catalase (an important antioxidant enzyme) production in mice showed a modest increase in lifespan, when important enzymes were knocked out in C. elegans (a model organism) there was curiously no reduction and reducing expression of various antioxidant mechanisms in mice also failed to reduce lifespan. While a certain amount of vitamins and antioxidant intake is necessary, as many are co-factors in essential reactions, it seems that aside from nutritional value there is little consensus regarding additional benefits.
Naked mole rats display lower antioxidant activity than normal mice, and yet live vastly longer lives and are extremely resistant to cancer.
When it comes to oxidative stress organisms also suffer differently. Short lived animals may suffer from different mechanisms, and longer lived creatures may have overcome these issues, only to suffer from another factor later on. We really don't know at this point; one mechanism might have positive effects in one organ, but none on another and in youth one factor may cause deterioration, but in older age it's something else. The picture is extremely complicated. People often like clear cut answers, requiring that a substance be beneficial across the board, when biology is such a complex interplay it's tough to work out cause and effect. The free radical theory is perhaps tempting because it offers a simpler 'cure' (as antioxidants are readily available), but it has not emerged as a strong contender for an overall mechanism.
There are also a number of other problems that complicate things when it comes to antioxidants:
- Many play a larger role in biology than simply antioxidant activity and act on multiple mechanisms e.g. vitamin C is a co-factor in collagen formation. You can't bunch all antioxidants together, because they do far more than simply quenching radicals, and vitamins shouldn't be confused with antioxidants (even if some are).
- They may be specifically harmful when a patient is suffering from cancer, as evidence suggests they can speed up tumor growth.
- While the overall free radical theory of aging may be tenuous, research on mitochondria has been a little more promising. Effectively the battery of a cell, the vast majority of free radicals arise within these tiny organelles. Antioxidants targeted to mitochondria are more specific than wider acting molecules like vitamin e or c.
- A problem with antioxidant mechanisms is that the body seems to use free radicals in signalling mechanisms. These molecules are supposed to warn the cell of failing organelles, allowing them to dispose of faulty machinery. By inhibiting and interfering with these systems, it may end up doing more harm than good, allowing damage to spread and linger on. Damaged mitochondria can act as a signal for cells to commit suicide, so blocking this mechanism might prove detrimental.
- The concept of hormesis contradicts some of the free radical theory. Essentially it argues that by exposing the cell to a sweet spot of stress, it up-regulates innate damage control responses and produces a net reduction in damage. Too much stress is still bad, but too little (i.e too much antioxidant protection) may down-regulate other protective mechanisms and leave the cell ill-prepared further down the road.
- Eating lots of vegetables in particular is widely supported, but benefits may be due to a wide ranging cocktail of chemicals rather than antioxidants. Plants contain thousands of different molecules, some of which may be anti-inflammatory or regulate certain genes differently. While they are often high in antioxidants, that may be a 'red herring', leading to incorrect assumptions about the reasons behind their benefit.
If you're feeling a little lost, you're not alone. While free radicals can certainly cause damage and antioxidants are certainly not altogether 'bad', it seems more probable that there's a balancing act at hand and that aging is far more complicated than was first imagined. Essentially data shows that for now a multivitamin doesn't compete with a varied and healthy diet.
Read more at The Scientific American