看了两段。
First of all, a shift worker needs to investigate carefully and understand thoroughly the negative impacts and implications of shift work. According to a workbook, Shift Work: Health Effects & Solutions, factors (加上that，这里的that不能省，省了就成错句子了） affect adaptation to shift work include: 1. Age; 2.Gender; 3. Previous Shift work experience; 4. Morning/night person; 5. Fitness Level; 6. Health Status; 7. Circadian Rhythm; 8.Contentment with the Job (Occupational Health Clinics for Ontario Workers Inc., 2005). All of these factors contribute to the mental and physical health of shift workers.
However, within among all these factors, the circadian rhythm plays a significant role. After millions of years of evolution, human beings have （我prefer这里用单数表集体概念，but no set rule） become a day-orientated species. People’s lives follow the cycle of the sun. People’s bodies are programmed by their biological clocks. These internal biological clocks govern human beings’ sleep-wake cycle. When a person is sleeping, complex physiological changes occur: 1.Body Temperature decreases.2.Heart rate and blood pressure decrease. 3. Kidney and bowel function is suppressed.4.Hormones for tissue restoration increase.5.Hormones that maintain wakefulness decrease (IARC, volume 98, 2010). In addition, there are distinct rhythmic changes in the course of a 24-hour period. For example, the heart rate and body temperature are typically the lowest around 4:00 am, and peak in mid-afternoon. Shift work is often opposite to the trend of circadian rhythm. This is one of the reasons why in the early morning, normally, the interval of 4:00 am is the most tired moment for shift workers. （这句怪，4：00am不是interval，估计你是指的4-5am, 如果是interval的话用moment不合适，tired修饰人可以，觉得修饰moment有点怪。建议： between 4 and 5 am, the shift workers are most tired/exhausted）Studies of new shift workers demonstrate dropout （dropout from the study？) rates of 20% at 1 year and 33% at 2 years (IARC, volume 98, 2010).
