It's a well-known refrain: Lack of sleep is harmful. But what does this really mean? And, more importantly, can the effects be reversed? This is a critical concern for resident doctors, whose schedules are comparable to those of shift workers. 

 

It’s not just feeling tired and sluggish

 

For doctors, sleep deprivation is not just about feeling sleepy. It's linked to decreased cognitive abilities, slower reaction times, and a propensity for increased medical errors. There's an increased sleepiness and irritability, a noticeable drop in empathy, a greater likelihood of motor vehicle accidents, and a tendency to rely more on substances that induce sleep. 

 

 

Sleep duration vs sleep quality

 

According to researchers writing in Frontiers in Epidemiology, sleep quality offers a more comprehensive assessment of sleep and daytime functionality than sleep duration alone.

Sethi P,P Pathania M, Gupta R, et al. Poor quality sleep is associated with greater carotid intima media thickness among otherwise healthy resident doctors. Front Epidemiology. 2023;2:1044111.

Although sleep duration is variable from person to person, the ideal duration lets a person feel refreshed upon waking and able to maintain efficient daytime functioning. Sleep duration is influenced by genetics, health status, environment, and substance use/abuse. 

 

Sleep quality, on the other hand, is mainly dependent (in young adults) on physical activity, social interaction quality, use of stimulants, stress levels, sleep-wake patterns, number of nocturnal awakenings, and total sleep time. Sleep disorders like insomnia, obstructive sleep apnea, and restless legs syndrome also significantly affect sleep quality.

 

The ideal number of hours

 

The relationship between sleep deficit and cardiovascular health is complex. Effects such as disruptions in the sympathetic nervous system, accelerated arterial stiffening, induction of a pro-inflammatory profile, and cardiac dysfunction may be involved.

The Frontiers in Epidemiology authors cite recent studies indicating that increasing the duration of sleep—particularly among college students and pre-hypertension individuals who lack sufficient sleep—benefits cardiovascular health. However, other research suggests that prolonged sleep duration elevates cardiovascular and cardiometabolic disease risk, by elevating blood pressure, blood glucose, and cortisol levels. 

 

In actuality, there appears to be a “sweet spot.” Both long (>9 hours/day) and short (<7 hours/day) lengths of sleep are associated with an elevated risk of metabolic syndrome, hypertension, diabetes, and cardiovascular mortality.

A nationwide study in 2023 revealed a U-shaped correlation between the length of sleep, systolic blood pressure (SBP), and the likelihood of developing CVD.

Yang S, Zhang N, Liang Z, et al. Examining the U-shaped relationship of sleep duration and systolic blood pressure with risk of cardiovascular events using a novel recursive gradient scanning model. Front Cardiovasc Med. 2023;10:1210171.

 

 

A study of residents

 

Among medical residents, 45% to 90% experience poor sleep quality. This poor sleep quality is linked to fatigue, stress perception, memory issues, and depression, among other complaints.

The article in Frontiers in Epidemiology reported on the authors’ investigation of the association between sleep quality and carotid intima-media thickness (CIMT), an established indicator of early atherosclerosis.

The top-three factors impacting sleep quality and these results were sleep-onset latency exceeding 30 minutes, sleep efficiency below 85%, and frequent sleep disturbances. 

Similarly, a report from Sleep Medicine also found a significant link between poor sleep quality and increased CIMT in stroke-free individuals.

Del Brutto OH, Mera RM, Zambrano M, et al. Sleep quality correlates with the carotid intima-media thickness in stroke-free community-dwelling adults living in rural Ecuador. The Atahualpa Project. Sleep Med. 2019;55:22-25.

Sleep quality was assessed by the Pittsburgh Sleep Quality Index score, and the study population consisted of people ≥40 years living in rural Ecuador. Symptoms of psychological distress like depression and anxiety were independently significant factors.

 

 

Erratic schedules

 

An erratic sleeping schedule, frequent among resident doctors and shift workers, is associated with circadian rhythm dysfunction.

Abu Farha R, Alefishat E. Shift work and the risk of cardiovascular diseases and metabolic syndrome among Jordanian employees. Oman Med J. 2018;33(3):235-242.

This disruption in the body's natural sleep/wake cycle is increased by psychosocial stress that can imbalance the autonomic nervous system, favoring the sympathetic nervous system in the muscular and thoracic regions and the parasympathetic division in the intra-abdominal area. 

 

Some epidemiological studies, including a meta-analysis, indicate a potential link between sleep schedule and CVD, with shift workers showing a 40% increased risk of ischemic heart disease compared with their daytime counterparts. 

A notable study involving over 27,000 participants from Sweden's Västerbotten intervention program found a substantial correlation between night shift work and metabolic syndrome. In addition, a study of post–acute myocardial infarction (MI) patients in China revealed that inadequate sleep significantly elevated the risk and severity of acute MI and coronary artery disease, with late bedtime further increasing AMI risk.

Lian X, Gu J, Wang S, et al. Effects of sleep habits on acute myocardial infarction risk and severity of coronary artery disease in Chinese population. BMC Cardiovasc Disord. 2021;21:481.

 

The important message from these studies is that by integrating intelligent sleeping strategies, everyone can improve their chances of achieving adequate rest, even amidst a demanding medical residency schedule.