Introduction
Infertility is a reproductive system disease that is characterized by
the inability to achieve a clinical pregnancy after 12 or more months of
regular unprotected sexual intercourse 1. According to
epidemiological surveys, the incidence of infertility is rising and
trending younger, affecting 186 million couples worldwide2, accounting for about 10%-15% 3,
with a prevalence of 25% among couples of reproductive age in China4, which has become the third most serious disease
affecting human health after cardiovascular diseases and tumors5. With the implementation of China’s fertility
policy, infertile individuals and couples are under pressure from
society, family, and the treatment process due to the long-term
inability to have children normally, causing great psychological burden
and social-emotional distress, which largely affects the physical and
mental health of infertility patients 6, 7.
Depression, one of the most prevalent mental disorders, is manifested by
persistent low mood, affects 4.4% of the global population
proportionally, or approximately 322 million people 8,
and is the second leading cause of disability worldwide9. Currently, it is well documented that depression is
closely associated with an increased risk of developing multiple
metabolic syndromes 10, including obesity11, hypertension 12, and
immuno-metabolic dysregulation 13, resulting in
long-term adverse health outcomes. However, regarding the comorbidity
phenomenon of depression and infertility, it is unclear whether this
simply reflects shared risk factors. There is speculation that
depression may be a cause of infertility, its consequence, or both14. A previous study reported a significant
association between depression and treatment outcomes in assisted
reproductive technology (ART) 15. As a matter of fact,
depression may be even more prevalent in infertile patients compared to
the general population of reproductive age 14,
considering the long course of infertility, complex etiology, many
cooperating factors, high treatment costs, cumbersome treatment process,
and the influence of social culture and traditional beliefs. There is
growing evidence that depression may be associated with multiple
factors, not only risk factors from social aspects but also
individual-level lifestyle factors, such as circadian rhythm
disturbances, which may play a significant role in the onset and
progression of depression and the overall severity of depressive
symptoms 16.
Accumulating evidence suggests that circadian rhythm disturbances are
associated with a number of adverse health outcomes17, including but not limited to obesity18, type 2 diabetes 19,
cardiovascular diseases 20, reproductive functions21, psychiatric disorders 22, and
cancer 23. The chronotype is generally considered to
be one of the manifestations of circadian rhythms, and it represents the
behavioral pattern of organizing events during the 24 hours of a day,
especially referring to the subjective preference of individuals for
sleep-wake times 24, 25, which can be divided into
morning chronotype, neutral chronotype, and evening chronotype26. In previous studies, it was agreed that evening
chronotype was a risk factor for mental health and that individuals with
morning chronotype were at lower risk of developing emotional problems
such as anxiety and depression compared to evening chronotype27. With the increasing prevalence of infertility,
more and more researchers are also focusing on circadian rhythm
variations in infertile individuals and have found that worse sleep
quality and evening chronotype are more common in infertile populations
compared to those with fertility 28. However, it is
noteworthy that two prospective studies exploring the onset and
progression of infertility from a chronotype perspective suggest
suggested that morning chronotype may be a risk factor for fertility29, 30.
To be sure, it is necessary to examine the impact of morning chronotype
on depression during infertility treatment. Since infertility is a more
specific reproductive disorder, although not fatal, it can have a
negative impact on the individual and the spouse, or even the entire
family. Depressive symptoms, a major type of depression, without timely
intervention are likely to develop into depression. Therefore, exploring
the causes of depression is essential to promote health and function
throughout the life course. To the best of our knowledge, there is a
lack of clarity about the relationships between chronotype and
depressive symptoms during infertility treatment. Accordingly, the
objectives of this study were (1) to examine the effect of sleep type on
the depressive symptoms in subjects undergoing infertility treatment.
and (2) to assess the partner effect of spouses’ chronotype on each
other’s depressive symptoms.