Cold-related health risks

Physiologically, thermal stress is any change in the thermal relation between a temperature regulator and its environment that, if uncompensated by temperature regulation, would result in hyper- or hypothermia (IUPS Thermal Commission, 2001). Thermal comfort is the subjective indifference to the thermal environment. The thermal comfort zone is the range of ambient temperatures, associated with specified mean radiant temperature, humidity and air movement, within which a human in specified clothing expresses indifference to the thermal environment for an indefinite period (IUPS Thermal Commission, 2001).

Weather and environmental conditions have an impact on thermal stress. The cooling effect of air flow (draught), air humidity or wind (wind chill) can increase the effects of cold and has a big influence on human thermal balance (Danielsson, 1996). On the other hand, during physical activity such as walking or cycling, thermal strain can increase, and clothes become wet also in the cold environment. Moist skin and wet clothes are not a good combination in a cold environment. Heat is produced in biochemical processes such as the oxidation of carbohydrates and fat in the human body. Heat is transferred from the inner parts of the body to the body surface by radiation, conduction, convection and vaporization (Hardy and Soderstrom, 1938). External heat flow from the skin to the environment can lead to the cooling of the body. Thermal strain may become high and increase the thermal stress levels of the body. Accumulated moisture in the clothing not only makes it wet but also causes uncomfortable thermal sensations and poses a health risk in cold conditions (Rintamaki and Rissanen, 2006).

Cold can have harmful effects on health and performance, and other environmental factors can make cold weather even more hazardous. A combination of wind, wet and cold ambient temperature can even lead to hypothermia if the exposure lasts for long and no protective garments are used (Thompson and Hayward, 1996). Cold tolerance differs depending on the person, and individual differences in thermoregulatory responses exist. Hypothermia is widely considered to be amore serious threat for older than younger persons because of older persons’ impaired ability to defend body temperature during cold exposure and preventable changes in body composition and physical fitness (Young and Lee, 1997). Cold temperatures can also affect the way pharmaceuticals work in the human body. For example, cold temperatures can lead to changes in the way widely used antihypertensive drugs are absorbed or distributed in or excreted from the body (Komu-lainen, 2007). This, in turn, means that cold temperatures influence the efficacy of pharmaceuticals. Thermal balance also has effects on human conscious responses and cognitive function (Flouris and Cheung, 2009; Makinen et al., 2006; Paakko-nen, 2010; Palinkas et al., 2005). It is important to note that nutritional and hydration statuses have impacts on thermal balance, both in hot and cold environments, and, therefore, dehydration of the body may expose people to injuries with both cases decreasing physical and cognitive performance (Marriott and Carlson, 1996).

Low ambient temperatures can expose individuals to severe health risks (Biem et al., 2003). Fatal hypothermia can happen even in relatively mild temperatures. Most mortality cases have been found to happen when the temperature of the environment is above 0° Celsius. According to physiological studies, an air temperature of 25°C exposes us to hypothermia. In water, the risk limit for hypothermia is even greater, being as high as 33°C (Brandstrom et al., 2012). Cold tolerance differs depending on the person and individual variation in thermoregulatory responses (Brandstrom et al., 2012). Our body temperature is regulated to remain close to a set point of 37°C. According to Parsons, the core temperature of the human body can vary safely only by 4.5°C (Parsons, 2003). Physiological functions in humans work properly in the zone between hypothermia (35.0°C) and hyperthermia (39.5°C). The thermo-neutral ambient temperature for naked, resting humans is approximately 27°C.

This means that this is the optimal temperature for humans to avoid body cooling: below 27°C, one has to move, or use another physiological mechanism such as burning brown body fat to produce body heat, or use external heat sources. Above 27°C, heat loss by evaporation begins, resulting in cooling (IUPS Thermal Commission, 2001). Thermal adaptation to cold (acclimatization or acclimation) takes approximately 2 weeks (IUPS Thermal Commission, 2001). Newly arrived displaced persons who are not used to cold temperatures often are unable to acclimatize fast enough to avoid health risks. Humidity and skin moisture increase the rate of body cooling (Holmer, 1993). This risk is particularly relevant if adequate shelter is missing.

Physiological stress induced by excessive cold can impair functioning of the body (Biem et al., 2003). Skin, hand and foot cooling can cause discomfort, pain or even cold injuries (Rintamaki et al., 1993). As was shown by Paakkonen, cold can change our mood and cognition, and it has effects on the pineal and thyroid hormones (Paakkonen, 2010). Cold can lead to accidental hypothermia or cold injuries if the risks are not observed and taken into account. Cold can have effects on general health or it can worsen the symptoms of existing medical disorders, such as diabetes mellitus (see e.g. Parsons, 2003; Rintamaki, 2007; Scott, Bennett, and Macdonald, 1987).

Cold can pose a risk to persons with specific health conditions. Problems with the circulation in hands and feet, previous frostbite, coronary artery disease, severe hypertension, severe symptoms in joints and muscles, severe infections, trauma, respiratory failure or some endocrine disorders may all cause increased sensitivity to cold (Biem et al., 2003). Also malnutrition increases the risk of hypothermia (Young et al., 1998). In general, it has to be noted that children and the elderly are particularly vulnerable because they are less capable of maintaining body temperature than adults under the age of 60 (Castellani and Young, 2016; Castellani et al., 2006; Young and Lee, 1997). In children, this is owing to the ratio of body surface to body mass, which means that they are likely to lose body heat quickly (Young and Lee, 1997). Children and older persons are likely to have difficulties when it comes to taking measures to protect themselves against cold (Castellani et al., 2006; Frank et al., 2000). The mortality risk is increased - for example, in cases of long-term cold exposure (e.g. in the case of homelessness) or substance abuse.