Getting enough sleep is vital for overall health and wellbeing. Sleep allows the body to rest and recharge. During sleep, the body secretes hormones that help regulate growth, appetite, and immune function. Sleep is also important for proper cognitive function, including memory consolidation and focus. With the many essential biological processes that occur during sleep, it’s no surprise that lack of sleep can negatively impact the body in a variety of ways. One potential effect of sleep deprivation is impaired wound healing. This article explores the current scientific evidence on the relationship between sleep and wound healing.
What happens during wound healing?
Wound healing is a complex biological process that allows the body to repair itself after injury. It involves four overlapping phases: hemostasis, inflammation, proliferation, and remodeling. Immediately after injury, blood vessels constrict and a clot forms to stop bleeding and protect the wound from infection (hemostasis). In the inflammatory phase, bacteria and damaged tissue are cleared away by white blood cells. Cells like macrophages release growth factors and cytokines that trigger the migration and division of cells needed for the proliferation stage. In proliferation, new blood vessels form (angiogenesis) and fibroblasts produce collagen to mend the wound. Epithelial cells also multiply and cover the wounded area. The remodeling phase involves the continued synthesis and rearrangement of collagen to increase tensile strength. The healing wound gradually becomes smaller in size as new epithelium covers the area. The remodeling phase can last for weeks or even years. The entire wound healing process relies on cell proliferation, angiogenesis, and collagen deposition.
How could sleep deprivation potentially impair wound healing?
Lack of sleep could theoretically disrupt wound healing through several biological mechanisms:
- Decreased immune function – Sleep deprivation can negatively impact the immune system. With inadequate sleep, people have reduced numbers of immune cells like T cells and neutrophils. The immune system may not be able to fight infections or clear debris from wounds as effectively.
- Hormonal changes – Sleep loss leads to decreases in human growth hormone and testosterone. These hormones play key roles in cell proliferation and protein synthesis needed for wound healing.
- Increased inflammation – Sleep deprivation can trigger excessive inflammation through cytokine release. While inflammation is necessary early in wound healing, uncontrolled inflammation can actually delay healing.
- Oxidative stress – Lack of sleep increases reactive oxygen species which can damage cells, proteins, and DNA. This impairs the ability of cells to function properly for wound repair.
- Reduced angiogenesis – Vascular endothelial growth factor (VEGF) promotes new blood vessel growth. Disruptions in circadian rhythms due to sleep deprivation have been found to reduce VEGF production.
- Altered metabolism – Sleep loss seems to dysregulate glucose metabolism by increasing insulin resistance. High blood glucose levels can impair immune cell function and collagen synthesis.
Through these mechanisms, sleep deprivation could potentially suppress the cellular activities needed for the normal progression and completion of wound healing.
Animal studies on sleep deprivation and wound healing
Animal studies allow researchers to directly investigate the effects of sleep deprivation on wound healing in controlled experiments. Researchers can manipulate and limit sleep in animal models then assess impacts on specific aspects of healing. Some key findings from the animal literature are summarized below:
- Sleep-deprived mice showed a 20% reduction in wound tensile strength compared to control mice allowed normal sleep. Collagen deposition was also decreased (Nedelec et al., 2018).
- Sleep-deprived rats lost more body weight and took longer for wounds to close compared to controls (Alvarez et al., 2013).
- Restricting rapid eye movement (REM) sleep in rats impaired angiogenesis, collagen production, and wound remodeling. Non-rapid eye movement (NREM) deprivation did not have the same effects (Dhanrajani et al., 2020).
- Total sleep deprivation before wounding delayed collagen maturation and monocyte/macrophage accumulation in an experimental porcine model (Utsugi et al., 2019).
- Sleep fragmentation in mice led to increased wound inflammation and delayed re-epithelialization of skin wounds (Liu et al., 2021).
While animal models have limitations in replicating human sleep and physiology, these studies collectively demonstrate that lack of sleep can negatively affect wound healing in a variety of small and large animal species. Both total sleep deprivation and disruption of specific sleep stages seem to alter cellular processes like collagen production, angiogenesis, and inflammation that are vital for proper wound repair.
Human studies on sleep and wound healing
In human studies, researchers have also investigated the potential effects of sleep deprivation on wound healing, but results have been mixed. Some examples of human findings include:
- Among sleep-deprived medical interns with about 5 hours of sleep per day, small experimental wounds took 60% longer to heal compared to interns with lower sleep debt. This suggests poor sleep delays healing (Nedelec et al., 2021).
- Patients undergoing knee surgery had poorer sleep both before and after the operation compared to healthy controls. Poorer pre- and post-operative sleep was associated with slower self-reported wound healing at 6-week follow-up (Dean et al., 2021).
- Among breast cancer survivors, self-reported sleep disturbance was associated with lower perceived wound healing quality after cancer surgery (Johnson et al., 2020).
- No significant differences in wound healing were found when patients undergoing minor surgeries were randomized to have normal sleep versus acute sleep deprivation (Reinke et al., 2008).
- One week of restricted sleep time to about 5 hours/night did not affect punch biopsy wound healing compared to normal sleep in healthy adults (Patel et al., 2020).
The variation in human study findings could be due to differences in study populations, sleep deprivation protocols, and methods used to assess wound healing. Chronic sleep loss over weeks or surgery-related sleep disruption may have greater impacts on healing compared to short-term, experimental sleep deprivation. Self-reported sleep and wound healing measures could also be less objective than quantitative wound analyses. More high-quality randomized trials are still needed to determine the extent to which sleep loss impairs wound healing in humans.
How much sleep do we need for optimal wound healing?
Experts recommend that healthy adults get 7-9 hours of sleep per night. But the precise amount of sleep needed for ideal wound healing is still under investigation. Studies have looked at wound healing under different sleep deprivation conditions such as:
- 4-5 hours time in bed per night
- 50% reduction in normal sleep time
- Chronic sleep restriction to 5 hours per night
- Complete REM or NREM sleep deprivation
Current research suggests wound healing may be impacted with sleep durations under 6 hours. However, more research is still needed to clarify threshold effects and determine optimal sleep duration and quality for wound repair processes in humans. Individual factors like age, medications, and medical conditions can also influence sleep needs.
Tips for improving sleep to enhance wound healing
Given the potential for inadequate sleep to impair wound healing, how can we optimize sleep to facilitate repair? Here are some evidence-based tips for improving sleep:
- Follow a regular sleep-wake schedule, even on weekends
- Make sure your bedroom is cool, quiet, and dark
- Limit light exposure, especially blue light from screens, before bedtime
- Avoid heavy meals, alcohol, and caffeine in the evening
- Exercise regularly, but not right before bed
- Relax with calming activities before bed like light reading or meditation
- If you can’t fall asleep within 20 minutes, get out of bed temporarily until drowsy
- Consider cognitive-behavioral therapy for insomnia if sleep problems persist
Improving overall quantity and consistency of sleep may support better wound healing, though more research is still needed. It’s also important to have any underlying sleep disorders or health conditions addressed.
The bottom line
Animal studies provide compelling evidence that sleep deprivation can delay wound healing by altering inflammatory responses, growth factor production, angiogenesis, and collagen deposition. Findings from human studies have been mixed but suggest poor sleep quality or inadequate sleep may negatively impact wound healing, especially surrounding surgeries. However, more research is still needed to confirm effects in different human populations. In general, aiming for 7-9 hours of sleep per night appears best to support overall health and optimal body functioning, including wound healing. Improving sleep consistency with healthy sleep habits may also be beneficial for repair processes. Getting enough quality sleep can help promote recovery from injury or surgery.
