According to the World Health Organization (WHO), health is defined as ‘a state of complete physical, social and mental well- being and not merely the absence of disease of infirmity’. This topic aims to develop among the students an understanding of biological knowledge of some factors affecting physical health. It is hoped that the knowledge gained can help increase students’ willingness to adopt good practices which contribute to physical health.

Diet

1. As heterotrophs we depend on the food we take in as the source of the chemical constituents required for the normal growth and functioning of the body.

2. Deficiency in particular constituent (e.g. mineral, vitamin, protein) will upset the normal functioning/ growth of the body.

3. Taking too much energy-rich food will result in problems like overweight or obesity because excess carbohydrates and fats taken in will be stored inside our body as fats.

We should also be aware that poor diet is sometimes associated with a higher risk of certain non-infectious diseases (e.g. diet containing a large amount of fats is associated with cardiovascular diseases).

Exercise

The amount of work the muscles can perform is limited by the amount of oxygen obtained during ventilation, and the efficiency of the cardiovascular system in supplying oxygen to the muscles. As the body is trained to be more efficient in obtaining oxygen and delivering it to the muscles, people who exercise regularly are able to accomplish regular activities easier ad respond more readily to sudden demands on physical activities.

1. The skeletal muscles increase in size, strength and capacity for work with regular and moderate exercise. The muscles involved in ventilation become stronger and thus the vital capacity of the individual is increased.

2. The heart muscle increases in size in response to training. The heart can beat stronger to increase the cardiac output.

3. With an efficient supply of oxygen, the high energy yield from aerobic respiration fuel the muscles to do work.

Rest

Continual activity (especially muscular activity) for a sustained period leads to accumulation of toxic wastes (e.g. lactic acid) and depletion of food reserve (e.g. glycogen). The importance of rest to health is allowing exhausted cells to undergo a period of inactivity or low activity for removing toxic wastes and replenishing the food reserve in the cells.

Alcohol abuse

To understand the immediate effects of alcohol, we have to know that alcohol is a depressant which slows down the activities of the central nervous system.

1. Alcohol slows down the speed at which nerve impulses are transmitted. This lengthens the reaction time of the affected person making him slow to respond.

2. The ability of an alcohol depresses the activity of the parts of the cerebrum controlling these functions.

Drinking large amounts of alcohol over a period of time can cause health problems such as malnutrition and hardening of the liver.

- Malnutrition may result in long-lasting alcoholism because alcoholic beverages are high in caloric content but law in nutritive value.

- Hardening of the liver is associated with alcohol abuse. Alcohol is mainly metabolized in the liver. The mechanism by which the hardening develops is still unclear, but it appears to involve the consequences of the metabolism of excessive amounts of alcohol.

Smoking

Substances in tar of tobacco smoke are carcinogenic. The risk of developing lung cancer is directly related to the amount of tar that gets into the lungs.

It is estimated that about a quarter of the deaths from coronary heart disease were associated with smoking. Nicotine and carbon monoxide in tobacco smoke are thought to be the major causes. Nicotine increases the workload of the heart, while carbon monoxide reduces the supply of oxygen to the heart. Both nicotine and carbon monoxide increase the tendency to develop blood clots within the blood vessels.