Nutrients (營養素)
A balanced diet is essential for good health (as well as exercise and not abusing drugs). The amout of the different types of food required varies with age, occupation and life-style. There are seven nutrients which are needed:
carbohydrates (醣類/碳水化合物 ) (e.g. sugar, starch) from bread/potatoes/rice provide energy
proteins from meat/fish/milk/cheese provide amino acids for growth and building and repairing cells
fats from butter/oil/margarine to store energy and provide energy when carbohydrates ran out
vitamins (vitamin C) and minerals (iron) from fruit/vegetables required in small amounts for many vital processes and hence good health
Water and fibre are also important. About 75% of a human body is water and all chemical reactions take place in water. Without water all cells will die. Fibre (roughage) is not digested but helps the digestive system by the production of faeces and prevents constipation. There is also evidence that fibre in the diet reduces risks of bowel cancer.
Vitamins and Minerals
Vitamins are chemicals that are required in the body, in small amounts, to control vital processes. Scurvy is a disease that causes bleeding gums and weakness in muscles, and can only be prevented by vitamin C. Vitamins and minerals required by the body are:
vitamin A from dairy products/fresh green vegetables/fish oils for good eyesight/growth/health skin
vitamin B1 from egg yolks/yeast for good nerves/growth
vitamin B2 from liver/yeast/milk to help digestion/nerves of skin
vitamin C from oranges/lemons/fresh green vegetables for healthy skin/resistance to disease
vitamin D from butter/eggs/fish oils for good bones and teeth
vitamin E from wheatgerm/green vegetables affects reproduction
calicum from milk/green vegetables for good bones and teeth
fluoride from milk and toothpaste for hardening tooth enamel
iron from red meat/liver/spinach for good haemoglobin
iodine from table salt/seafood for thyroid gland in the neck
sodium from table salt nor proper function of nerves
potassium from cereals/fresh green vegetables for muscles
magnesium from fresh green vegetables for muscles
Food Additives
Food additives are used by food manufacturers for various reasons such as making the food look good; from going bad; improve flavour; reduce the costs of ingredients and keeping the ingredients thoroughly mixed. Approved food additives are given E numbers:
E100-E180 are colour agents, both artificial and natural
E200-E290 are preservatives to stop microbes growing in the food
E300-E321 are anti-oxidants to stop air turning the food bad
E322-E494 are emulsifiers to ensure that the ingredients remain mixed
Some food additives could cause medical problems including allergies.
Microbes (微生物)
Germs (病菌) or pathogens (病原) such as bacteria (菌) and viruses (病毒) are microbes (microscopic organisms) that cause illness. Once entered the body cells, they reproduce rapidly causing damage to the healthy cells while bacteria also produce large quantities of poisonous waste substances called toxins (毒素). Toxins are carried around the body in the blood, producing symptoms of the disease. Cholera is a disease caused by a bacteria and measles is a disease caused by a virus. Meningitis (腦膜炎) and influenza (流感/流行性感冒) can be caused by bacteria or virus. Viruses cannot survive long outside human cells but bacteria can grow and reproduce outside living organisms. Antibiotics (抗生素) can kill bacteria but has no effect on viruses.
Bacteria are very small living cells about 1/100th of the size of body cells with no nucleus and the bacteria DNA in the cytoplasm. Bacteria cause illness by producing toxins and damaging healthy cells. However, some bacteria are useful in helping digestion. Food Poisoning, Tetanus, Whooping Cough and Sore Throats are caused by bacteria.
Viruses are not cells but a coat of protein around a DNA strand (a piece of genetic information). They are very very small (1/100th the size of a bacterium) and cause illness by invading the nucleus of healthy cells to replicate themselves and damaging the healthy cells. Colds, Flu, Chicken Pox, German Measles and Polio are viruses.
White blood cells protect the body against microbes. Phagocytes kill bacteria by engulfing them. Lymphocytes produce antibodies to neutralise the bacteria and viruses and the toxins produced by them. Antibodies increase the body's immunity against microbes because they recongise the foregin bodies. Immunity against a particular microbe (bacteria or virus) is having the right antibody. Antibodies can be gained either naturally or artificially. Nature immunity is where the antibodies are passed on from the mother or the initial antibodies are generated by the body itself when first infected by the microbes. Artificial (or acquired) immunity is by immunisation where dead microbes are injected into the body causing antibodies to be made so that the body is ready to produce these antibodies when a real infection occurs.
Smoking and alcohol
Tobacco contains an addictive drug called nicotine which speeds up the heart rate, narrows the arteries and raises blood pressure thus increasing the chance of heart disease. The tar in the inhaled smoke coats the lining of the lungs reducing the intake of oxygen and the carbon monoxide renders the red blood cells incapable to transport oxygen.
Smoking also affects the lungs' self-cleansing mechanism of mucus removal by slowing down the movement of the cilia (moving hairs) that move the mucus up the throat. This causes mucus to collect in the bronchioles causing 'smoker's cough'. Germs can more easily get into the lungs, making diseases such as bronchitis more common. The lungs can be permanently damaged if it is not cleared up. If the bronchioles become narrow then breathing will be more difficult. The alveoli break up to form large air spaces, reducing the surface area which can absorb oxygen. Breathing needs to be faster to receive the same amount of oxygen. This is an illness known as emphysems and will eventually be fatal.
The tar in smoking contains carcinogens (致癌物) which causes lung cancer. Even non-smokers suffer from the health risks of tobacco due to 'passive smoking' inhaling the smoke from nearby smokers.
Alcohol is a depressant drug that slows down the drinker's reactions, although in small amounts can reduce inhibitions and boost confidence. With large amount, coordination is clumsier, vision can become impaired causing judgement errors and uncontrollable behaviour. For these reasons, there is a severe limit on the concentration of alcohol permitted in a driver's blood. However, it is not possible to know precisely when the alcohol concentration is below the limit as each person uses up alcohol at different rates. Roughly a half pint of beer, a glass of wine and a single whisky all contain one unit of alcohol. Drinking alcohol is addictive and continuous excessive consumption damage the brain and liver.
Drugs
There are four types of drug which affect the nervous system that controls the operation of the body:
- sedatives/depressants slow down the responses of the nervous system causing slow reactions and poor judegement of speed/distances. Examples are barbiturates (巴比妥類藥物) and alcohol.
- stimulants tend to make the nervous system more alert and strong stimulants give a feeling of boundless energy. Caffeine is a mild stimulant whereas amphetamine and methedrine are strong stimulants.
- hallucinogens cause a person to have experiences which are not real or different from real-life. Examples are LSD and ecstasy.
- pain-killers which remove the sense of pain. Examples are aspirin, morphine and heroin, the latter two are extremely addictive.
Some drugs are useful, such as penicillin (antibiotics) and aspirin (for many minor illness) and has medical use but drug misuse/overuse has harmful effects. Many drugs are addictive which can seriously affect the long-term health. Some drugs such as aspirin, caffeine and antibiotics are legal whule most are illgeal (cannabis, speed (amphetamine) and ecstasy).
Drugs are not medicine but most medicines contain drugs. Hot lemon cold remedies may contain the drug paracetamol. Alcoholic drinks contain the drug alcohol which is not a medicine.