the mid afternoon. Effects on life Hormones In diurnal animals, it is typical for blood levels of the hormone cortisol—which is used to increase blood sugar, aid metabolism and is also produced in response to stress—to be most stable in the afternoon after decreasing throughout the morning. However, cortisol levels are also the most reactive to environmental changes unrelated to sleep and daylight during the afternoon. As a result, this time of day is considered optimal for researchers studying stress and hormone levels. Plants generally have their highest photosynthetic levels of the day at noon and in the early afternoon, owing to the sun's high angle in the sky. The large proliferation of maize crops across Earth has caused tiny, harmless fluctuations in the normal pattern of atmospheric carbon dioxide levels, since these crops photosynthesize large amounts of carbon dioxide during these times and this process sharply drops down during the late afternoon and evening. Body temperature In humans, body temperature is typically highest during the mid to late afternoon. However, human athletes being tested for physical vigor on exercise machines showed no statistically significant difference after lunch. Owners of factory farms are advised to use buildings with an east–west (as opposed to north–south) orientation to house their livestock, because an east–west orientation generally means thicker walls on the east and west to accommodate the sun's acute angle and intense glare during late afternoon. When these animals are too hot, they are more likely to become belligerent and unproductive. Alertness The afternoon, especially the early afternoon, is associated with a dip in a variety of areas of human cognitive and productive functioning. Notably, motor vehicle accidents occur more frequently in the early afternoon, when drivers presumably have recently finished lunch. A study of motor accidents in Sweden between 1987 and 1991 found that the time around 5:00 pm had by far the most accidents: around 1,600 at 5:00 pm, compared to around 1,000 each at 4:00 pm and 6:00 pm. This trend may have been influenced by the afternoon rush hour, but the morning rush hour showed a much smaller increase. In Finland, accidents in the agriculture industry are most common in the afternoon, specifically Monday afternoons in September. One psychology professor studying circadian rhythms found that his students performed somewhat worse on exams in the afternoon than in the morning, but even worse in the evening. Neither of these