Antioxidants: A Radical Story.
With the rising incidence of obesity in the UK, there has been an increasing demand for new, affordable but effective treatments, and also preventative precautions. Being obese can raise the risk of developing cancer and cardiovascular disease (CVD), which have some of the highest mortality rates of all diseases found in the UK (2). Therefore, much research has focused on addressing these issues, and how to reduce their mortality rate.
Both cancer and CVD are linked with a series of chemical reactions inside the body, collectively known as oxidative stress. Oxidative stress occurs due to the fact that the electrons on molecules are only stable when found in pairs; a free radical is a molecule with an unpaired electron. Free radicals are highly reactive, and will take one electron from another stable molecule becoming stable themselves, but in doing so leave the other molecule with a free radical. This free radical can only be donated to another molecule, if that molecule has a free radical itself. Otherwise, electrons will continuously be removed from stable molecules, generating new ones in the process. The loss of an electron from a molecule is known as oxidation; hence oxidative stress. Free radicals can react with and damage DNA, resulting in mutations. Mutations in genes involved in regulating cell division can result in unregulated replication, a hallmark of cancer. Should a free radical react with low density lipoproteins (LDLs; complexes of proteins and lipids which transport cholesterol in the blood), cells called macrophages will absorb the resulting material to form a plaque which is deposited along the walls of blood vessels, narrowing them. This is known as atherosclerosis, and can cause cardiovascular disease, or even strokes, by inhibiting the blood flow to vital organs (3).
Antioxidants are molecules which can inhibit or eradicate oxidative stress within the body (4). They are oxidised in preference to molecules like DNA and LDLs, reducing the magnitude of damage to these molecules. There are many types of antioxidants, including carotenoids, phyto-sterols, flavonoids, and polyphenols (3). Carotenoids are a sub-class of vitamin A, and are regularly found in red and yellow coloured fruits and vegetables, such as peppers, mangoes, oranges, carrots, and red palm oil. They are also present in wholegrains, spinach, and broccoli. Other forms of vitamin A also act as antioxidants, and can be found in liver, egg yolk, and oily fish (5). One sub-class of vitamin C, called dehydro-ascorbic acid may also act as an antioxidant. This is added to many foods as a preservative, where it prevents the oxidation of some lipids found in food, which would otherwise go rancid (6). Other antioxidants can be found in tea, coffee, dark chocolate, and darker berries (3).
A lot of research has been carried out in an attempt to discover whether a diet high in antioxidants could prevent cancer and CVD. Some studies suggest that there is a correlation (4). One such study used a group of 805 men, between the ages of 65 and 84 years old. Their diet histories were carefully studied. The daily mean baseline intake of antioxidants of the group was 25.9mgs, which came mostly tea, onions, and apples. After five years, 43 men had died of heart conditions, and 38 suffered heart attacks (some of which were not fatal). The study found a statistically significant inverse relationship between flavonoid (an example of an antioxidant) intake and deaths caused by coronary heart disease. This correlation remained after adjustment for factors such as age, physical activity and blood pressure. Due to the convincing correlation with the amount of anti-oxidants consumed, it was concluded that there was significant evidence for a link between the consumption of antioxidants, and the reduced risk of heart disease (7).
There are also studies that suggest that antioxidants have their disadvantages too. For example, it is known that polyphenols will bind to minerals like iron and zinc in the digestive system, preventing their absorption into the blood stream (3). Other studies say that if too many antioxidants are consumed frequently, they may damage cells, and not aid them (8).
Currently, there is no proven link between antioxidant consumption, and the health benefits described above (8). A healthy balanced diet will automatically allow the consumption of antioxidants, as fruit and vegetables are especially rich in these compounds. It should be considered that antioxidants are phytonutrients; in nutrition terminology, these are chemicals which may prove beneficial for health, but are not essential for survival, and are mostly derived from plants. It is far more important to consume enough essential nutrients such as vitamins and minerals, as well as protein, lipids, and carbohydrates, instead of focusing on antioxidants. The fact that a diet containing too many antioxidants may be detrimental to health should also be taken into consideration.
Those who suffer from cancer and CVD should seek more detailed advice from a dietician.
By Emma Steer, 2nd Year BSc Nutrition
- 1. The Gout Killer, 2015, Antioxidant Rich Diet [online], date accessed [14/07/2015], https://thegoutkiller.com/gout-diet/antioxidant-rich-diet/
- 2. NHS, 2014, The Top 5 Causes of Premature Death [online], date accessed [14/07/2015], http://www.nhs.uk/Livewell/over60s/Pages/The-top-five-causes-of-premature-death.aspx
- 3. Maycock J, 2015, Anti-Nutritional Factors and Phytonutrients [online], date accessed [14/07/2015], https://vlebb.leeds.ac.uk/webapps/blackboard/content/listContent.jsp?course_id=_406093_1&content_id=_2895102_1
- 4. Aspden W, Caple F, Reed R, Jones A, Weyers J, 2011, Assaying Active Phytochemicals in Functional Foods, pages 428-430, Practical Skills in Food Science, Nutrition, and Dietetics, Pearson Education Limited, Essex
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- 7. Hertog MGL, Feskens EJM, Kromhout D, Hertog MGL, Hollman PCH, Hertog MGL, Katan MB, 1993, Dietary Antioxidant Flavonoids and the Risk of Coronary Heart Disease; The Zutphen Elderly Study, Volume 342, Pages 1007-1011, The Lancet [online], date accessed [14/07/2015], http://www.sciencedirect.com/science/article/pii/014067369392876U
- 8. Medline Plus, 2015, Antioxidants [online], date accessed [14/07/2015], http://www.nlm.nih.gov/medlineplus/antioxidants.html