In addition to being able to squeeze in a few extra miles of running, one of the biggest changes that I was able to make in my training regimen when I finished my PhD and became a full-time athlete was getting a lot more sleep. Endurance athletes push their bodies to the limit when training and preparing for competitions, and it is widely accepted in the running community that getting enough rest is critical to let your body recover and adapt after hard workouts so that the training can have the desired effect and lead to improved performances. Additionally, getting enough sleep is associated with good health in the general population and government organisations (e.g. the NHS in the UK and CDC in the US) typically offer advice on improving sleep habits in order to get sufficient amounts. I can't know exactly how much of an impact the extra sleep had on my running, but I definitely improved my performances over the next 2 years and I also very rarely found myself missing training sessions due to illness. Recently I haven't been managing to get quite as much sleep as usual, and I believe that this was probably a contributing factor to the sinus infection which led to me dropping out halfway round the NYC Half Marathon last month. In addition to less sleep, I was also exposed to more potential pathogens than normal as I was commuting on public transport to a temporary work placement. I'm no longer working, have been trying to make sure that I get more sleep, and thankfully seem to have returned to full health again.
Following this recent experience, I decided that I would like to know a little bit more about the effects of sleep deprivation - both on our abilities to train and perform optimally in sports, and also on our general health. I have to admit that this isn't something that I had given a great deal of thought to in the past, mainly because the requirement for sleep seemed too obvious to justify spending much time thinking about the reasons behind it. In a similar way to the feelings of hunger which remind us that eating is crucial to our health, there is a homeostatic drive to sleep which becomes greater the longer that we stay awake - i.e. we feel increasingly tired. The importance of sleep is further demonstrated by the fact that over time this homeostatic drive becomes strong enough to initiate brief 'microsleeps' even when a person is active1 and sleep at that moment may in fact be dangerous, as in the case of drivers falling asleep at the wheel. However, although there are numerous scientific articles which demonstrate the depth of research carried out in the field (and at least one journal dedicated entirely to sleep), there currently does not seem to be a definitive answer to the question of why we sleep. What is clear is that this research has created an ever-growing body of evidence which indicates that sleep deprivation plays a role in a multitude of health issues.
One side effect of sleep deprivation, which I had already heard about, is an increased risk of obesity and diabetes2. There is in fact a bidirectional relationship between lack of sleep and these diseases: sleep deprivation can lead to metabolic and hormonal changes which cause insulin resistance and increases in appetite, but pyschological factors and anatomical abnormalities (e.g, sleep apnea linked to excess weight) in diabetic and/or obese people can then interfere with sleep quality and lead to a worsening of health problems. Although weight gain is not usually something that an athlete running 100+ miles a week has to worry about, probably of greater interest to the endurance athlete are the immune effects of sleep deprivation which are associated with an increased risk of insulin resistance and also cardiovascular disease. Results vary between different studies, but it is generally found that sleep deprivation leads to an increase in the circulating numbers of blood cells involved in inflammatory immune responses, as well as raised levels of inflammatory signalling molecules (cytokines)3. This raised inflammatory state in subjects getting inadequate levels of sleep has the potential to affect sporting performance, and is one reason why sleep should be a high priority for all athletes.
Increased levels of inflammatory cytokines such as interleukin-6 (IL-6) are hypothesised to play a role in the development of overtraining syndrome - unexplained fatigue and underperformance in athletes during training periods4. This underperformance, and the related but less severe condition referred to as overreaching, generally occur as a result of heavy training volumes without sufficient rest and recovery. When the stress of heavy training is amplified by additional stress factors, such as the pressures of major competitions or a lack of adequate sleep, an athlete's training load is more likely to result in the development of symptoms of overreaching. Although the increased inflammatory immune response associated with sleep deprivation is likely to be one component involved in development of this syndrome, many other factors are thought to play a role as well. In fact, there is also evidence for a role of immune suppression or modulation in the development of fatigue5. This actually highlights another method for sleep deprivation to lead to overtraining syndrome, because in addition to a general state of increased inflammation a lack of sleep is also associated with disrupting the the balance of protective immune responses. The seemingly conflicting affects of reduced sleep are in part due to the fact that the sleeping period is split into different stages, during which different biological processes occur. The early stage of sleep is actually associated with induction of protective inflammatory immunity, which is then dampened down in later sleep stages prior to waking6. Disruption of sleep can therefore impede the generation of protective targeted immune responses, while simultaneously causing additional health problems through the generation of widespread non-specific inflammation.
The importance of a non-disrupted sleep cycle for the initiation of protective inflammatory immune responses takes us back to the idea that adequate sleep is desirable to help prevent athletes from missing training and races due to illness. Experimental evidence for an impact of sleep on the development of immunity has been demonstrated in studies that have found an association between sleep after vaccination and the generation of a protective immune response 7,8. Although more research does need to be carried out, there is definitely evidence to suggest that getting sufficient sleep can improve our bodies' abilities to fight off infections and remain healthy. Indeed, the International Society of Exercise and Immunology mentions sleep in a list of 'practical guidelines for prevention of infections among athletes':
As can be seen from the length of the above list, sleep is only one of a large number of factors that can impact the immune health of athletes. However, it is also one aspect of training that is often quickly neglected due to other pressures and commitments. Most people want/need to work and have some kind of social life outside of sport, but if you're serious about achieving your athletic targets then sometimes you might need to say no to that Happy Hour drink after work, drag yourself away from Facebook/Twitter and tuck yourself into bed an hour or two earlier!
1Poudel et al. Losing the struggle to stay awake: Divergent thalamic and cortical activity during microsleeps. Human Brain Mapping. 2012 Sep 24 (Epub ahead of print).
2Lucassen et al. Interacting epidemics? Sleep curtailment, insulin resistance, and obesity. Annals of the New York Academy of Sciences. 1264(1): 110–134, 2012.
3Mullington et al. Sleep Loss and Inflammation. Best Practice & Research: Clinical Endocrinology & Metabolism. 24(5): 775-784, 2013.
4Kreher and Schwartz Overtraining Syndrome: A Practical Guide. Sports Health. 4(2): 128-138, 2012.
5Silverman et al. Neuroendocrine and Immune Contributors to Fatigue. PM&R. 2(5): 338-346, 2010.
6Besedovsky et al. Sleep and Immune Function. Pflugers Archiv. 463(1): 121-137, 2012.
7Lange et al. Sleep after Vaccination Boosts Immunological Memory. Journal of Immunology. 187(1):283-90, 2011.
8Prather et al. Sleep and Antibody Response to Hepatitis B Vaccination. Sleep. 35(8): 1063–1069, 2012.
Increased levels of inflammatory cytokines such as interleukin-6 (IL-6) are hypothesised to play a role in the development of overtraining syndrome - unexplained fatigue and underperformance in athletes during training periods4. This underperformance, and the related but less severe condition referred to as overreaching, generally occur as a result of heavy training volumes without sufficient rest and recovery. When the stress of heavy training is amplified by additional stress factors, such as the pressures of major competitions or a lack of adequate sleep, an athlete's training load is more likely to result in the development of symptoms of overreaching. Although the increased inflammatory immune response associated with sleep deprivation is likely to be one component involved in development of this syndrome, many other factors are thought to play a role as well. In fact, there is also evidence for a role of immune suppression or modulation in the development of fatigue5. This actually highlights another method for sleep deprivation to lead to overtraining syndrome, because in addition to a general state of increased inflammation a lack of sleep is also associated with disrupting the the balance of protective immune responses. The seemingly conflicting affects of reduced sleep are in part due to the fact that the sleeping period is split into different stages, during which different biological processes occur. The early stage of sleep is actually associated with induction of protective inflammatory immunity, which is then dampened down in later sleep stages prior to waking6. Disruption of sleep can therefore impede the generation of protective targeted immune responses, while simultaneously causing additional health problems through the generation of widespread non-specific inflammation.
The importance of a non-disrupted sleep cycle for the initiation of protective inflammatory immune responses takes us back to the idea that adequate sleep is desirable to help prevent athletes from missing training and races due to illness. Experimental evidence for an impact of sleep on the development of immunity has been demonstrated in studies that have found an association between sleep after vaccination and the generation of a protective immune response 7,8. Although more research does need to be carried out, there is definitely evidence to suggest that getting sufficient sleep can improve our bodies' abilities to fight off infections and remain healthy. Indeed, the International Society of Exercise and Immunology mentions sleep in a list of 'practical guidelines for prevention of infections among athletes':
- Check athletes are updated on all vaccines needed at home and for foreign countries should they travel abroad for training and competition
- Minimise contacts with infected/sick people, young children, animals, and potentially contaminated objects.
- Keep at a distance from people who are coughing, sneezing, or have a 'runny nose'; and, when appropriate, wear or ask them to wear a disposable mask.
- Wash hands regularly, before meals, and after direct contact with potentially contagious people, animals, blood, secretions, public places, and bathrooms. Carry alcohol-based gel with you where lavatories are not available or not clean enough.
- Use disposable paper towels and limit hand to nose/mouth contact when suffering from upper respiratory tract or gastrointestinal symptoms.
- Do not share drinking bottles, cups, towels, etc.
- While competing or training abroad, prefer cold beverage from sealed bottles, avoid crude vegetables, and meat. Wash and peel fruits before eating.
- Quickly isolate a team member with infection symptoms and move out his/her roomate.
- Protect airways from being directly exposed to very cold and dry air during strenuous exercise, by using a face mask.
- Ensure adequate levels of carbohydrate intake before and during strenuous or prolonged exercise in order to limit the extent and severity of the exercise-induced immunosuppression phase.
- Wear proper out-door clothing and avoid getting cold and wet after exercise.
- Get at least 7 hours sleep per night.
- Avoid crash dieting and rapid weight loss.
- Wear flip-flop or thongs when going to the showers, swimming pool and locker rooms in order to avoid dermatological diseases.
- Keep other life stresses to a minimum.
As can be seen from the length of the above list, sleep is only one of a large number of factors that can impact the immune health of athletes. However, it is also one aspect of training that is often quickly neglected due to other pressures and commitments. Most people want/need to work and have some kind of social life outside of sport, but if you're serious about achieving your athletic targets then sometimes you might need to say no to that Happy Hour drink after work, drag yourself away from Facebook/Twitter and tuck yourself into bed an hour or two earlier!
1Poudel et al. Losing the struggle to stay awake: Divergent thalamic and cortical activity during microsleeps. Human Brain Mapping. 2012 Sep 24 (Epub ahead of print).
2Lucassen et al. Interacting epidemics? Sleep curtailment, insulin resistance, and obesity. Annals of the New York Academy of Sciences. 1264(1): 110–134, 2012.
3Mullington et al. Sleep Loss and Inflammation. Best Practice & Research: Clinical Endocrinology & Metabolism. 24(5): 775-784, 2013.
4Kreher and Schwartz Overtraining Syndrome: A Practical Guide. Sports Health. 4(2): 128-138, 2012.
5Silverman et al. Neuroendocrine and Immune Contributors to Fatigue. PM&R. 2(5): 338-346, 2010.
6Besedovsky et al. Sleep and Immune Function. Pflugers Archiv. 463(1): 121-137, 2012.
7Lange et al. Sleep after Vaccination Boosts Immunological Memory. Journal of Immunology. 187(1):283-90, 2011.
8Prather et al. Sleep and Antibody Response to Hepatitis B Vaccination. Sleep. 35(8): 1063–1069, 2012.
