Seasonal variation in physiological responses to mild cold air in young and older men

Eight men aged 60–65 years and six men aged 20–25 years, wearing only swimming trunks, were exposed to an air temperature of 17° C and 45% R.H. in each of the four seasons. The increase in the rate of metabolic heat production $\left( {\% \Delta \dot M} \right)$ for the older group in the cold test was significantly higher in summer and autumn than in winter and spring (P<0.05), but did not differ in the young group between seasons. Compared to the young group the $\% \Delta \dot M$ was significantly greater for the older group (due to a marked increase in four individuals) in summer and autumn (P<0.04). At the end of the period of cold exposure, the decrements of rectal temperature (ΔT _re), mean skin temperature ( $\bar T_{sk} $ ; due to a marked decrease in four individuals) and foot skin temperature (T _foot) were significantly greater for the older group compared to the young group at all times of the year (P<0.003). Seasonal variations in the two groups were similar, e.g., theΔT_re gradually became smaller from summer to winter (P<0.05) and then increased slightly in the spring (P=0.07).T _foot for both groups decreased from summer to autumn (P<0.01) and remained unchanged subsequently. No seasonal variations were observed for $\bar T_{sk} $ in either group. The increase in diastolic blood pressure (BP_d) during the test was significantly smaller in winter in both groups (P<0.05). BP_d became larger again during spring in the older group (P<0.01), but remained low in the young group. The BP_d was significantly greater for the older group than the young group in winter and spring (P<0.05). Compared to young men these results suggest that older men may lose the tolerance acquired by earlier cold acclimatization as seen by the BP_d responses, and have a somewhat lower thermoregulatory capability in coping with mild cold air in all seasons.