Free radicals are generated by our body by various processes including breathing, digestion, exercising, stress, pollutants, smoke, fumes, chemicals and so on. There are many types of free radicals, however, Reactive Oxygen Species (ROS) are the ones of most concern in biological systems. ROS are generated constantly as part of normal life and they are necessary for normal cell functioning and cell signaling.
For example, white blood cells, such as neutrophils, produce oxygen free radicals to kill invading pathogens. Burning fat for energy is also a type of oxidization called lipid peroxidation which we will discuss later in this article. However, these free radicals become harmful if created in excess and if there are inadequate antioxidant defences to combat them. Like many processes in the body, it is a fine balance, and it is when this balance gets out of kilter that problems start to happen. When free radicals are present in excess of the defence mechanism’s ability to control them, they can become toxic and damage starts to occur. Free radicals are both a cause and a result of inflammation.
Damage from free radicals causes inflammation and chronic inflammation produces more free radicals which in turn, creates more inflammation. This is a vicious cycle which takes its toll on the body, resulting in poor health outcomes. In addition, as we age, we naturally produce more free radicals and therefore, free radical damage increases with aging. This is part of the life process. Unfortunately, there is no way to stop the aging process, but we can give our bodies a helping hand by ensuring we consume plenty of foods that are rich in anti-oxidants to help combat excessive free radicals and maintain a healthy balance.
A balance between free radicals and antioxidants is necessary for proper, healthy functioning of our systems. When free radicals overwhelm the body's ability to regulate them, we get a condition known as oxidative stress. Basically, this is caused by an imbalance between antioxidants and the reactive oxygen species, which results in damage to cells or tissues. Recent studies have reported that oxidative stress is involved in the development of many other human diseases and aging. For example, there is considerable evidence that suggests that oxidative stress results in inflammation and tissue damage in the respiratory system. Indeed, research shows that Reactive Oxygen Species have been attributed to an aggravating role in the inflammation that accompanies asthma.(1) There are many simple dietary interventions that can significantly reduce oxidative stress and potentially prevent or at least minimize the development of asthmatic symptoms.
There is increasing evidence that oxidative stress is involved in the development of Alzheimer’s(2) and Parkinson’s.(3). However, it is not clear if oxidative stress is the cause or consequence of these neuro-degenerative diseases because there are multiple mechanisms involved. Alzheimer’s disease is the most common neuro-degenerative disorder, and its incidence increases with age. Increased production of reactive oxygen species, reduced antioxidant systems, and decreased efficiency in repairing mechanisms have been linked to Alzheimer's disease (4). The brain is particularly susceptible to oxidative damage. It requires a lot of energy to power the neurons and therefore needs a constant supply of oxygen and glucose. At rest, it uses approximately 20% to 23% of the body’s total energy requirements, despite accounting for only 2% of the body’s mass. It also consumes approximately 20% of the total body oxygen which is used to metabolize the glucose and use it for fuel. The brain is also very rich in easily oxidizable polyunsaturated fatty acids as well as iron and ascorbate, which are key players in oxidation and facilitate the formation of oxygen free radicals. The brain is also characterized by a low level of antioxidants.
Oxidized LDL can produce inflammation in the arteries promoting atherosclerosis, which increases the risk of heart disease and stroke. The oxidation of LDL occurs when free radicals react with the LDL cholesterol in the body. This can produce tissue damage in the surrounding area and triggers the inflammatory response and inflammatory cells, such as macrophages. Both this inflammation and the by-products of the inflammatory process can slow or completely restrict the amount of blood flowing through the blood vessel, which results in poor health outcomes.
As we can see, oxidative stress is implicated in many chronic diseases, and is also a part of the normal ageing process. Oxidative stress increases with age and it is increasingly likely to overwhelm our natural repair systems. This is a major contributor to diseases associated with aging and with the onset of disease, free radical production increases further. It is now well established that biological aging correlates with the accumulation of these oxidized bio-molecules in most tissues. Therefore, it is important for us to have enough antioxidants in the system to combat these free radicals and prevent oxidation. That is why they are called antioxidants because they prevent this oxidization.
Lipid peroxidation is the metabolic process in which reactive oxygen species cause the oxidative deterioration of lipids. A well known toxic effect of ROS is damage to cellular membranes, which is initiated by the process of lipid peroxidation. What are lipids? Lipids are fat-like molecules and make up the building blocks of the structure and function of living cells. The main biological functions of lipids is to produce energy when metabolised. Lipids also form the structural components of cell membranes and form various messengers and signalling molecules within the body.
Fats, and the fatty acids from which they are made, are lipids. A primary target for peroxidation is polyunsaturated fatty acids and, specifically, omega 6 fatty acids. So if we are eating a high level of omega 6, then we are creating a much bigger target for these ROS.
The Anti-oxidant Defense System
Antioxidants are molecules that are capable of stabilizing or deactivating free radicals before they attack cells. Humans have evolved highly complex antioxidant systems which work synergistically, and in combination with each other to protect the cells and organ systems of the body against free radical damage. The antioxidant defense system of the body consists of enzymatic and non-enzymatic compounds.
The enzymatic antioxidants include superoxide dismutases, catalase and glutathione peroxidase. The non-enzymatic antioxidants include vitamins A, C and E, beta carotene, coenzyme Q10, glutathione and phenolic compounds. However, the modern diet often doesn't contain enough anti-oxidants to maintain the balance. Eating your fruit and veg is a good way to get natural dietary antioxidants but we may need more and taking supplements is a good way to ensure we have enough reserves. Once we've used up all of our antioxidants, the free radicals have the upper hand and take over. The balance has tipped and there is nothing to stop them causing cellular damage. That is why it is really important to get a daily intake of antioxidants to keep our reserves topped up.
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