To our knowledge, this is the first study of the relationship between sleep behaviour and depression in older age in a large nationally representative study. We found that sleep duration, the presence of sleep problems and sleep disorders were strongly associated with depression. We then learned that too little sleep, a higher proportion of older people with sleep problems or sleep disorders, and older patients with poor sleep patterns were at greater risk of depression.
Among the 436 older depressed patients, older women (61.7%) were about 1.6 times more likely than older men (38.3%). One study reported[27] that older women reported significantly higher levels of depression than men, which is consistent with our findings. There are many reasons why older women are more likely to be depressed than older men. After the menopause, women's oestrogen levels decrease, which can be associated with increased mood swings and depressive symptoms[28]. Studies have shown that in[29], Women may be more sensitive to certain genes that affect the risk of depression. Second, older women may be more likely to experience certain life events, such as living alone and having children away from home, which can increase the risk of depression. Women are more likely to choose social withdrawal or self-attribution when they face problems, and these strategies may be associated with the development of depression. Finally, older women may take on more caring responsibilities at home, which can lead to stress or depression.
Among older people without depression, 73.2% did not have sleep problems and 26.8% did. This suggests that older people with sleep problems are more likely to develop depression. There are many reasons why older people with sleep problems and sleep disorders are more likely to develop depression. Long-term sleep problems cause chronic stress, which is a known risk factor for depression. Lack of sleep can make it harder for the body and brain to recover, increasing mental stress. Sleep disorders can lead to reduced daily activities in older adults, as they may avoid social activities due to fatigue[30]. This social isolation increases loneliness, which in turn increases the risk of depression[12]. Sleep problems can affect older adults' quality of life, including daily activities, work productivity and overall well-being. These factors can increase the risk of depression. Inconcentration and reduced performance due to daytime sleepiness may trigger reactive depression, a response to life stressors[31]. At the same time, older people may have multiple chronic conditions, the management of which can affect sleep and mood, increasing the risk of depression. It is therefore very important to identify and treat sleep problems in older people with sleep disorders to reduce the risk of depression. At the same time, older people with depression also need to be assessed for the presence of sleep disorders and consider treatment options.
Short sleep duration increases the risk of depression in older adults, while longer sleep duration is not statistically significant, which may be related to their physiology. The National Sleep Foundation recommends[32] For older adults (65 + years), the recommended minimum amount of sleep per night is 7–8 hours. Lack of sleep can lead to moody mood, fatigue, irritability, forgetfulness, cognitive deficits[33], as well as obesity[34], diabetes[35] and hypertension[36], which may increase the risk of depression in the elderly. With the increase of age, the elderly body function decline, organs and tissues gradually decline, the metabolic capacity of the body, the body control body sleep hormones also began to slowly decline, seriously affect the elderly sleep, lead to difficult to sleep at night, insomnia increased significantly, thus shortening the sleep time at night[37]. Although studies have shown that sleeping too much or too little can increase the risk of depression, it is natural for older people to lose sleep due to reduced physical function. As the number of older people who sleep too long is not large, it is not statistically significant here.
Older adults with moderate sleep quality had a 2.49 times higher risk of depression than those with healthy sleep quality, while those with poor sleep quality had a 6.76 times higher risk of depression than those with healthy sleep quality. The results remained stable after adjustment for demographics, smoking, alcohol use and comorbidities, suggesting that poor sleep quality increases the risk of depression in older adults. Insomnia is the most common sleep problem in older people, manifesting as difficulty falling asleep, waking up frequently during the night, or waking up early. Insomnia and depression share common risk factors, and both are associated with serotonin and norepinephrine deficiency, hypothalamic-pituitary-adrenal axis hyperactivity, hyperexcitability, disturbed rapid eye movement (REM) sleep, and reduced slow-wave sleep[38, 39]. In addition, poor sleep quality affects older people's cognitive functions, including attention, memory and decision-making, which are also typical of depression[40]. Studies suggest that poor sleep quality may be a symptom of depression, and that depression may also cause or worsen sleep problems[41]. This bidirectional relationship means that sleep problems and depressed mood can influence each other, creating a vicious cycle.
Our study used data from a nationally representative sample of the population. The NHANES sampling method ensures that the sample is randomly selected and representative of the entire US population. The current study also has some limitations. First, as a cross-sectional study, the nature of the design does not allow us to determine whether sleep problems caused depression, or depression caused sleep problems, or both may have been influenced by common factors; second, data were collected at a single point in time and could not capture trends in sleep and depression over time. Finally, the reliance on participant self-report may be affected by recall bias, where participants may not be able to accurately recall past sleep or emotional states.