How Weather and Climate Affect Health

The elements and the climate we live in can have important effects on our health, and often in complex and unforeseen ways.

The human body is specially adapted to survive in the many different environments of the world. We can live equally succesfully in the extreme heat of the Sahara desert as in the snowy wastelands of Alaska. The body also makes short-term adjustments to cope with a change of climate. Variations in skin pigmentation, for example, occur when moving from a cool and cloudy to a hot and sunny environment.


If you normally live in a cold climate and then move to a sunny one, and you are fair-skinned, then you tan in response to the sun’s rays. This tanning is an important physiological response, because the increase in skin pigmentation associated with tanning provides protection for the skin and underlying tissues against the damaging effects of the sun’s ultraviolet (U V) rays. UV-induced problems include skin cancer, blistering and burning of the skin. Dark-skinned people such as indigenous Africans and Asians are adapted to their hot climates by having a permanently pigmented skin. It is when light-skinned people settle in sunny climates that problems arise. The Australian state of Queensland, for example, which has a large immigrant population, has one of the highest rates of skin cancer in the world.

The ultraviolet rays of the sun also have a beneficial effect on health, however: vitamin D, which is essen-tial for healthy bones, is synthesized by the body through the action of ultraviolet radiation on the skin. Insufficient amounts of this vitamin can lead to rickets, although the condition has become increasingly rare in Western countries.


We are also able to control our internal body tem-perature to a large extent, keeping it within the range 36°C to 37°C (97°F to 98°F), regardless of the environmental temperature. This is achieved through main-taining a balance between the amount of heat produced by metabolic reactions, such as digestion, and acquired by the body from the environment with the amount of heat lost to the surroundings. The reason we must keep our body within this narrow temperature range is because it constitutes the ideal conditions for the normal cellular activities which keep us alive. So, for example, if your body is exposed to heat and you become hotter than the outside environment (which usually is the case), the vessels carrying blood to the skin dilate. The increased blood flow near the skin allows you to lose heat to the outside air (and you look flushed). You can lose heat quite comfortably in this manner in temperatures up to around 30°C. On the other hand, if the outside temperature is cold, then blood flow near the skin is reduced to conserve heat and you therefore look pale. Sometimes, if the environment is very cold, a reduced blood flow to the skin is not in itself capable of main-taining the ideal internal body temperature. The body’s metabolic rate has then to increase to produce more internal heat. This requires energy and explains why we need to eat more in winter than in summer. In extreme circumstances, if the outside temperature goes below freezing, the blood vessels can constrict so much that exposed parts of the body, such as hands and feet, suffer tissue damage. If exposure is prolonged, frost bite may cause fingers and toes to swell, blacken and eventually drop off because they are no longer being supplied with blood. To help prevent tissue death, heat can be generated through exercise and even shivering. When the muscles are activated in this way they ‘burn’ glucose , the product of which is heat.

During severe cold, people sometimes use alcohol to make themselves feel better. Indeed, the cold is less intensely felt after a few drinks. This is because alcohol causes the blood vessels to dilate and so increases the amount of blood flowing to, for example, the fingers.

Black people are more susceptible to frostbite than white people because their bodies are inadequately equipped to deal with cold conditions. In contrast, Eskimos are able to maintain high body temperatures in extreme cold. They do this by raising their internal temperature through high metabolic activity. This means that they need to consume large amounts of food to provide sufficient energy and also explains why they are usually fat, since fat is weight-for-weight the best food source of energy. The fat layer under the skin has the additional advantage of providing insulation against the cold.

Obese people thus have fewer problems in keeping their body temperature at acceptable levels when it is very cold than thin people. On the other hand, they have more difficulty in lowering their body temperature when it is warm as their insulating fat layer pre-vents rapid heat loss. When the weather is warm slender people are far better off. The absence of a thick fat layer makes it more easy for them to radiate excess body heat. Moreover, thin people have more skin surface in proportion to body weight than fat people, which allows for a relatively large area of the body to be cooled.

In terms of survival, the body’s response to heat is not as important as its ability to combat extreme cold. Unless there is no water supply available, hot conditions are rarely lifethreatening. Human endurance of hot climates is thought to be as much a behavioural phenomenon as a purely physical one; people soon learn to avoid physical work during the hottest part of the day and take periods of rest (siestas) instead, and also to wear light, comfortable clothing. If the outside temperature goes much above 30°C the body’s sweating mechanism starts to operate at maxi-mum force. Water from sweat glands in the skin evaporates into the air, which draws heat from the body. If the outside air is humid, however, this process of evaporation is impaired and stops altogether at extremely high humidity. This is why high tempera-tures can be tolerated much better when the humidity is low than when it is high. In humid conditions, the sweat literally drips down the body and you feel sticky and uncomfortable.

On moving to a warmer climate, the ability to produce sweat increases as more sweat glands come into operation; along with the acquisition of a tan this consti-tutes an adaptive response, a bodily acclimatization to a warmer environment. It appears that the ability to sweat is similar in all races.

Oxygen and atmospheric pressure

Another example of adaptation to the environment concerns altitude. At high altitudes the atmospheric-pressure is low, which means that there is less oxygen available in the air. The body tissues thus do not receive as much oxygen as usual, with the result that if you move from a low altitude to a high one you get tired more quickly.

Artificial methods can be employed to compensate for the change in atmospheric pressure, such as in a pressurized aircraft cabin or the use of oxygen cy-linders by montaineers. Without artificial assistance, the body adapts to the deficit in atmospheric oxygen by more rapid breathing, and (over several weeks) by producing more oxygen-carrying red blood corpuscles. There is also an increase in the number of capillary blood vessels in the lungs, muscles and brain. Races who live high above sea level, such as the Tibetans who live at above 3,000 metres, often have wide, deep chests with extra breathing capacity. Deleterious effects of short-term changes in atmospheric pressure are sometimes experienced by deep-sea divers who work in suits or chambers filled with compressed air. The high pressure causes more oxygen and nitrogen than usual to dissolve in the blood. This may interfere with normal cellular activity, impair brain function, and affect behaviour. Drowsiness and inefficiency are common. Very severe problems can occur when the diver is raised too quickly to the surface as the decreased pressure causes nitrogen to form bubbles in the tissues and fluids. This decompression sickness, also known as caisson disease or ‘the bends’, has very serious effects and causes intense pain. Is is prevented by slowly decompressing divers, by gradually bringing them to the surface or keeping them in a slowly depressurizing room for several days.

Weather sensivity

Someone is called ‘weather sensitive’ when their nervous system (which regulates, among other body functions, heart-beat, digestion and respiration) reacts to changes in weather conditions. These reactions can include tiredness, headache, a decrease in concentration, disturbed sleep patterns and nervous tension. Moreover, there are certain physical phenomena which may be aggravated by the weather, such as corns, rheumatic pains, migraine headaches and asthma. In many cases psychological and physical reactions are interrelated. For example, many people become excitable just before a storm. A storm is often preceded by a sudden decrease in air pressure. This causes a relatively high pressure to develop in body cavities, which may become even higher with exercise, leading to a general feeling of agitation. Another, less explicable, example of the influence of the weather on human behaviour is known as the ‘Squall-illness’. It would appear that just before the occurrence of a squall (a warm mountain wind at the lee-side of a mountain range), the number of social-medical incidents, for instance, suicides, increases along with industrial and traffic accidents.

Climate and risks to health

Many of the disorders that afflict mankind are related to the weather and climate. Cold temperatures decrease the formation of antibodies which are the body’s natural defence mechanism. The common cold, influenza and infections of the upper respiratory tract, occur more frequently in cold weather. Bronchitis is particularly liable to occur in cold, damp, and foggy weather, causing a feeling of constriction in the chest and difficulty in breathing. Asthma, which also causes difficulty in breathing, may be more prevalent in some sufferers during the winter months; although hot weather can aggravate the condition in those people sensitive to increased levels of pollen in the air during summer.

Susceptible people may be troubled every summer by complaints such as watery eyes, sneezing and sniffing. The cause of these symptoms, known collectively as hay fever, is commonly an allergic reaction to pollen from various kinds of grasses. An attack of hay fever is usually brief, and is more irritating than disabling. For chronic sufferers, however, the condition may be more or less permanent during the spring and summer months. In these cases drugs designed to combat histamine, a product of the allergic reaction, may be found to be helpful in alleviating symptoms.

Cold also seems to aggravate rheumatic diseases, with a corresponding increase of pain felt in joints, muscles, and ligaments, leading to a loss in mobility. Thus, old people who suffer from rheumatic diseases benefit from being wrapped up warmly. Hypothermia occurs when there is progressive cooling of the body as a result of prolonged exposure to cold. In freezing water, where the body is unable to maintain its temperature, death may follow. Where exposure to cold is less severe, Raynaud’s syndrome which causes the extremities of the body, such as fingers, to become cold and white and lose sensation, is a commonly experienced problem. Extreme heat can also be a cause of illnes. Excessive sweating without adequate replenishment of the lost water (and salt) leads to deranged body functions. The changes induced may vary from relatively benign heat cramps to heat exhaustion or even to a sunstroke. In extreme causes of sunstroke the victim becomes nauseous and may faint, in a reaction very similar to that produced by shock. Recovery is usually swift, however, once the person has cooled down sufficiently.

Diseases from certain bacterial infections are also more common in hot climates because these organisms thrive on warmth. Also, food spoils more quickly in warm conditions and the chances eating contaminated food and contracting food poisoning, are high. Insects also thrive in hot climates, and mosquitoes, for example, can transmit malaria. Thunderstorms are another aspect of the weather that, on rare occasions, can be extremely dangerous. If you are struck by lightning during a storm you may be badly burned and the electrical voltage may kill. If lightning threatens, you should: . stay indoors and away from open doors and windows, electrical appliances and water. If you are outdoors and there is no shelter you should take the following precautions: . keep away from isolated trees, . avoid hilltops, wire fences and anything which conducts electricity, . in an open field do not lie down flat on the ground, but squat with the feet close to each other, . if possible, get into a car or a caravan which offer an excellent protection, because the metal exterior conducts the electrical current along the outside to the ground (rubber tyres do not hinder the process!). If hit by lightning, the victim should receive prompt medical attention since internal burns are likely. Snowblindness is also a direct consequence of environmental conditions: the sun reflects off the snow and damages the eyes to cause burning and swelling of the eyelids and intolerance to light. The damage to the eyes is caused by U V-rays. Protecting oneself from the elements is largely a question of common sense. Wear snow goggles on a skiing holiday, for example, or give yourself a few days to acclimatize when moving to new temperatures or altitudes. Observe local behaviour and customs such as the noontime ‘siesta’ in hot countries. The lack of foresight in not taking these basic precautionary steps is well summed up in the old song title: ‘Mad dogs and Englishmen go out in the midday sun!’.

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