Cardiovascular disease at the forefront of winter mortality

Cardiovascular diseases represent a major cause of mortality due to cold during the winter, according to a report by the Institute of Health Surveillance (VS) on the cold and health.

InVS conducted a literature search on due to health effects of low temperatures during winter.

Many studies have demonstrated the existence of a V-shaped curve between temperature and mortality with a steeper slope on the side of the high temperatures on the cold side. However, in absolute terms, the cold is deadlier than heat. Thus, mortality cold beyond the scope of some annual deaths from hypothermia homeless.

Seasonal variations with a winter peak is observed in several diseases such as coronary heart disease, stroke (stroke) and respiratory diseases. Mortality from these diseases, and increases almost linearly as the temperature decreases.

In January 1985, France has experienced a wave of unprecedented cold has led to significant mortality of 13%, mainly due to myocardial infarction (17%), for stroke (54%) and pneumonia (208%) it is appearing more sense.

the physiology of adaptation to the pathology of inadequacy

The human being protects against the cold through thermo endogenous physiological mechanisms involving the cardiac and respiratory nervous, endocrine,. Heat loss when the ambient temperature is low, increase to a body surface area ratio / high body mass (as is the case with children).

In France, there is no precise definition of the meteorological concepts of cold and cold, although thresholds at -5 and -10 ° C have been adopted by the plan "winter emergency" Secretariat to the fight against insecurity and exclusion. The wind is also a factor causing heat transfer. Thus, a wind of 90 km / h associated with a temperature of -10 ° C results in the same sense that a temperature of -30 ° C in calm weather.

Of adverse health effects appear if the thermoregulatory system is deficient or if the thermal stress is too high.

On the cardiovascular system, vasoconstriction due to cold and associated phenomena can lead to rupture of atherosclerotic plaques and thus promote the blockage of an artery by a thrombus (clot).

In the coronary arteries spasm related to cold associated with a possible thrombosis and increased demand for myocardial oxygen promotes the patient at risk, the occurrence of angina or myocardial infarction when complete stenosis of the lumen. In fact, about half of the excess winter deaths is attributable to coronary thrombosis. The interval between a cold snap and impact on cardiovascular mortality is 7 to 14 days.

In the brain, several mechanisms, namely hypertension, hyperviscosity and thrombosis may be the cause of ischemic stroke triggered by cold.

... without forgetting: respiratory infections, asthma and hypothermia

Other conditions that may be attached to the cold such as respiratory diseases include infections and asthma, as well as hypothermia affecting mostly the homeless and people under the influence of psychoactive substances or the alcohol.

If it has long been recognized as respiratory diseases increase in winter, the pathogenesis is still not fully understood, although inhalation of cold air irritating to the mucosa and the confinement of the population for the spread germs, are possible explanations. In fact, respiratory infections account for about 25% of excess winter deaths. The interval between a cold snap and impact on respiratory mortality is 15 to 30 days.

Furthermore, although the cold air inhalation is a trigger or exacerbation of asthma, cold however does not impose itself as a major risk factor compared to its impact on viral lung infections occurring in asthmatics.

Populations most at risk

The greatest concern in terms of public health conditions appear to be cardiovascular disease, respiratory infections and asthma, hypothermia and carbon monoxide poisoning, says InVS after the entire bibliography consulted in the preparation of this report.

For each of these conditions, especially sensitive populations were identified: the elderly, patients with ischemic heart disease to cardiovascular complications, respiratory failure and asthma to respiratory infections, with a special interest in children with asthma.

Poisoning Carbon concern, in turn, the general population as well as the disadvantaged population.

However, questions remain about the relationship between cold and human health: they relate to the choice of the best weather indicator (absolute or perceived another variable temperature), the relationship between this indicator and the frequency of specific conditions on the population groups for which this relationship should be studied, the geographical specificity of these relationships, and finally, the role of other factors (winter epidemics, air pollution ...). They justify further studies to determine if the cold-related illnesses are preventable and by what means.