Effects of outdoor temperature on changes in physiological variables before and after lunch in healthy women

Previous studies of autonomic nervous system responses before and after eating when controlling patient conditions and room temperature have provided inconsistent results. We hypothesized that several physiological parameters reflecting autonomic activity are affected by outdoor temperature before and after a meal. We measured the following physiological variables before and after a fixed meal in 53 healthy Japanese women: skin temperature, systolic and diastolic blood pressure, salivary amylase, blood glucose, heart rate, and heart rate variability. We assessed satiety before and after lunch using a visual analog scale (100 mm). We recorded outdoor temperature, atmospheric pressure, and relative humidity. Skin temperature rose significantly 1 h after eating (greater in cold weather) (P = 0.008). Cold weather markedly influenced changes in diastolic blood pressure before (P = 0.017) and after lunch (P = 0.013). Fasting salivary amylase activity increased significantly in cold weather but fell significantly after lunch (significantly greater in cold weather) (P = 0.007). Salivary amylase was significantly associated with cold weather, low atmospheric pressure, and low relative humidity 30 min after lunch (P < 0.05). Cold weather significantly influenced heart rate variability (P = 0.001). The decreased low frequency (LF)/high frequency (HF) ratio, increased Δ LF/HF ratio, and increased Δ salivary amylase activity imply that cold outdoor temperature is associated with dominant parasympathetic activity after lunch. Our results clarify the relationship between environmental factors, food intake, and autonomic system and physiological variables, which helps our understanding of homeostasis and metabolism.