Antioxidants for recovery: time to think pink?

Chemically speaking, oxygen is amazing stuff. Its special reactivity provides us with the energy required to sustain life, including the ability to power movements and muscular contraction. This explains why oxygen - and the ability to absorb, transport and use it - is so important to athletes, who need lots of it to sustain maximum power and work outputs.

However, the oxygen molecule is a double-edged sword, because this same chemical reactivity can also wreak cellular havoc by means of the transient, highly reactive and potentially destructive molecular species called ‘free radicals’, which are produced unavoidably as a consequence of harnessing the chemical energy of oxygen within the body. Free radical damage (see box 1) is now believed to be a major factor in aging, degeneration and many other diseases associated with age⁽¹⁾.

Box 1: What is free radical damage?

Free radical damage describes the damage that occurs within cells - for example to cell membranes and DNA (see figure 1) - at a molecular level as a result of ‘free radicals’. These free radicals are fleeting but extremely reactive chemical species that unavoidably occur during oxygen metabolism when fats, proteins and carbohydrates are combined with oxygen in the body to produce energy (aerobic metabolism). For this reason they are sometime called ‘reactive oxygen species’ (ROS) or ‘oxygen radicals’.

Although our cells have very efficient antioxidant defence systems to quench and neutralise harmful free radicals, these systems are not 100% efficient, and over time biochemical damage gradually accumulates, leading to a reduction in cellular function. Most scientists now believe that accumulated cellular free radical damage lies at the heart of the ageing process and many degenerative diseases such as cancer, autoimmune diseases and Alzheimer’s disease. 

Athletes process and use larger volumes of oxygen and at higher rates than the majority of the population; this explains why many scientists have assumed that they may benefit from higher intakes of antioxidant nutrients to bolster defences. Unsurprisingly perhaps, there are now dozens of antioxidant supplements on the market, some of which are aimed squarely at endurance sportsmen and women such as cyclists, runners, swimmers, triathletes etc. The reasoning is that these types of athletes might need greater antioxidant support because during long training sessions, their bodies process a lot more oxygen and generate more free radicals than the average couch potato.

Fortunately, the human body comes equipped with a number of systems capable of deactivating the free radicals produced as a result of oxygen metabolism, and dissipating their energy harmlessly. Collectively known as the ‘antioxidant defence system’, these systems use both antioxidant enzymes (large protein molecules manufactured in the body) and antioxidant nutrients (consumed in the diet) to mop up unwanted free radical activity and ‘soak up’ this potentially disruptive energy, thereby minimising damage to the body.

Athletes and antioxidants

In recent years, there has been much research into athletes, who not only consume more oxygen than others to fuel their training but also frequently train at or near their maximum oxygen uptakes, and who are at increased risk of free radical-induced damage, or ‘oxidative stress’^(2,3). Athletes don’t just process a larger volume of oxygen than their sedentary counterparts – they also process it at a higher rate; during training, the rate of oxygen processing by the mitochondria (the energy producing furnaces in the cells) can rise by a factor of 20, placing exceptionally high demands on their antioxidant defence systems.

In particular, there’s been much interest in nutrients that can help bolster the body’s innate antioxidant defence systems (eg glutathione peroxidise, which requires the mineral selenium to function⁽⁴⁾) as well as nutrients that can boost antioxidant activity in their own right (for example, naturally occurring bright colored plant phytochemicals founds in a wide range of fruits and vegetables⁽⁵⁾).

Given the importance of optimum muscular performance for athletes, a lot of the research into antioxidant protection for athletes has focussed on the ability of antioxidant nutrients to help protect against muscle damage during hard training. This exercise-induced muscle damage often manifests as delayed-onset muscle soreness (DOMS) as well as delayed or reduced recovery from training and competition⁽⁶⁾. In previous SPB articles, we have highlighted a range of these research findings, including:

•    Reduced muscle soreness after shuttle running when taking vitamin C⁽⁷⁾.
•    Reduced exercise-induced DNA damage in immune cells in exercising women when taking vitamins C and E⁽⁸⁾.
•    Enhanced muscle damage repair in older runners running downhill when taking vitamin E⁽⁹⁾.
•    Lowered markers of free radical damage and boosted activity of protective antioxidant enzymes in the body when taking alpha lipoic acid and N-acetyl cysteine (NAC)⁽¹⁰⁾.
•    Reduced markers of free radical damage following exercise when runners took methylsulfonylmethane (often abbreviated to MSM)⁽¹¹⁾, when ultra-distance runners and climbers took coenzyme Q10⁽¹²⁾ and when elite young footballers took astaxanthin (a naturally occurring pink-coloured compound found in yeast some fish/shellfish)⁽¹³⁾.

Box 2: Fruity protection

In addition to antioxidant nutrients such as vitamins C and E, and the mineral selenium, there’s also been a lot of research into fruit phytochemical antioxidant supplementation to enhance athletic performance and recovery. In cyclists for example, black grape (81 grams per litre [g/L]), raspberry (93g/L) and redcurrant (39g/L) concentrates reduced DNA damage compared to cyclists not taking the fruit concentrates⁽¹⁴⁾. Meanwhile, chokeberry juice reduced free radical damage in rowers undergoing strenuous exercise bouts⁽¹⁵⁾ and tart cherry juice was found to reduce muscle damage and DOMS in distance runners performing a 26km (16.2-mile) run⁽¹⁶⁾. Scientists believe that it’s the high levels of various natural phytochemical compounds (eg anthocyanins) found in berries and cherries that make these fruits particularly effective as antioxidants.

Something fishy

Eagle-eyed readers will have noticed that one of the antioxidant nutrients mentioned above is rather unusual in that it is neither a vitamin/mineral nor a plant phytochemical. Although it is a carotenoid compound and is therefore chemically related to the carotenoids beta-carotene and lutein found in orange and red vegetables such as carrots and tomatoes (see figure 1), astaxanthin is actually a dark-red carotenoid compound found in aquatic animals such as salmon and shrimp. Like plant phytochemicals, humans cannot synthesize astaxanthin and can only acquire it and benefit from it via dietary intake.

Figure 1: Astaxanthin, beta-carotene and lutein*