Seasonal Health Effects
The first warm rays of the spring sun magically seem to improve your sense of wellbeing. It is no secret that seasonal weather changes have a strong impact on human health. We know extreme heat and cold makes us sick, that summer brings sunburns and winter brings coughs and sneezes. Scientists delved into the subject of the seasons and our health a little deeper, and found some astonishing relationships.
Researchers correlated death rates from several diseases with the dates of the death and observed the trend. Infectious diseases, heart problems and strokes peak in winter. Extreme heat events show short-term peaks in death rates from heart-related disorders. On the average, however, winter cold appears to increase the rate of death from almost all diseases. A noticeable exception is cancer, which is equally spread amongst the seasons. The seasonal variability of death rates was greatest amongst the elderly above 60 years of age. Also, men appear to be more susceptible to cold influences, while women succumb to heat extremes more often.
There are regional differences, though. In climates with few dramatic temperature changes, death rates from infectious diseases showed most seasonal fluctuations. Changes in local weather conditions, such as the onset of the wet or dry season in the tropics, impact on the numbers of disease carriers and the survivability of viruses and bacteria.
Researchers took a further step and correlated birthdays with birth rates. Surprise! They observed marked seasonal variations. The birth of animals almost always follows the seasons. But in their case, the availability of food dictates evolution. Human reproduction appears to follow some other rules. For example, statistics show a lowering of the conception rate by 6% to 10% after a period with temperatures of up to 10 degrees above average. A low sperm count is to blame. This should reflect in fewer births during spring, and it does. Whether the fertility of women is also influenced by seasonal weather changes is unclear.
The birth rate may be lower, but springtime produces the heaviest and largest newborns. Babies born in spring are taller and heavier than those born during other months. Danish mothers, giving birth in this season, find their bundle to be an average 2.2mm longer than those from mothers giving birth in winter. Eighteen-year-old Austrian soldiers with springtime birthdays are on average 6mm taller than their companions born in autumn. Austrian researchers speculate that a difference in sunshine hours during pregnancy is a factor.
Seasonal factors also appear to affect the fetal and infant mortality rates, and the numbers of babies born with defects. Infant mortality peaks during summer heat-stress periods. More infants with diabetes are born during spring and early summer; and more schizophrenia appears amongst babies born in late winter and spring. Infectious diseases during the winter months, the seasonality of hormone changes, and nutritional or environmental factors, are all possible causes.
Winter is the season of colds, influenza and respiratory diseases. No secret here? Yes, there is. Like humans, bacteria and viruses prefer a warm climate. So why do they cause widespread outbreaks during winter? The winter months are generally more humid and have less UV radiation. Germs love the moisture and hate the sterilizing effect of the sun’s radiation. We also tend to spend more time indoors where the germs can accumulate. In addition, low temperatures in winter stress the immune system. Invaders encounter weakened defences.
A season with warm and humid weather breeds disease carriers such as the mosquito. In the tropics, the wet season is host to a variety of infectious diseases. Warm and dirty drinking water is also a breeding ground for viruses and bacteria. Hot summers in temperate regions often signal outbreaks of food poisoning. Poor food storage and handling techniques lead to rapid growth of bacteria numbers.
If the first warm rays of the spring sun magically improve your sense of wellbeing, you obviously belong to the 50 per cent of the population, which bursts with energy and euphorically embraces the new season. Others are not so fortunate. The other half of the population doesn’t want to get out of bed. For them, the new season brings lethargy, tiredness, and exhaustion.
The medical profession is not entirely clear on what causes spring-time lethargy, but several factors play a role:
- Powerful hormones. With an increase in daylight hours, the level of the sleep hormone melatonin drops, in favour of an increase of the daytime hormone serotonin. Initially, the hormonal shift may not keep up with the increasing daylight hours. The result could be symptoms similar to the “winter blues” or Seasonal Affective Disorder (SAD).
- Four seasons in one day. In spring, the intensity of weather elements such as temperature, air pressure, humidity, wind and sunshine hours, fluctuate frequently and sometimes extremely. The whole body is under stress, and tiredness and lethargy could be the consequence.
- Winter dormancy. Not everyone skis down the slopes in winter. For many, the wintry conditions could be an excuse for a sedentary lifestyle and overindulgence in calorie-rich food. Add to this a lack of fresh fruit and vegetables, and it shouldn’t come as a surprise that many lack energy when spring arrives.
- Hypotension. When the thermometer climbs, the blood vessels widen to improve the heat exchange between body and air. As a result, vasodilation, as the process is formally known, reduces the blood pressure. This affects everyone, but people with an underlying low blood pressure feel the symptoms most. This could include fatigue, depression, tiredness, and a lack of concentration.
To improve your mood, make use of days with sunshine and be active outdoors. The sunlight adjusts your hormone levels and exercise in fresh air will invigorate your cardiovascular system. Early-season fruit and vegetables appear on the market and make it easier to complement your diet with vitamin-rich and fresh food.