Saliva | Illness Prediction

Whenever you engage in a prolonged or intense bout of exercise, your spit takes on vastly different characteristics. One of the key changes in post-exercise saliva is a decline in the levels of an important protective chemical produced by your immune system – Immunoglobulin A (IgA). Because of IgA’s ability to ‘glom’ onto incoming viruses and destroy them, IgA is considered one of the first lines of defence against upper-respiratory infections in both athletes and sofa spuds. Its drop-off after strenuous workouts – or after several hard days of training – has been of concern to knowledgeable coaches, athletes, and sports scientists, who believe that the inverse relationship between hard training and IgA concentrations may help to explain why serious athletes have a heightened risk of colds and other respiratory illnesses during the weeks leading up to their major competitions. In a recent study, researchers at the Hunter Immunology Unit and the Royal Newcastle Hospital in Australia followed 26 elite swimmers over a seven-month training period and compared changes in their IgA levels, psychological stress, and infection rates with the changes observed in a group of 12 moderately exercising control subjects(1). As expected, salivary IgA concentrations displayed an inverse correlation with the number of infections in both elite swimmers and moderately exercising controls; the lower the average IgA, the higher the frequency of infection. In fact, when IgA levels fell by 6%, one additional infection (above the average) could be expected during the seven-month training period. The total number of infections an athlete could expect to experience over the course of seven months was predicted quite well by a simple statistical model which included just two factors – preseason salivary IgA levels and the average pretraining salivary IgA concentrations (‘pretraining’ simply means the IgA levels observed just before workouts commenced); pretraining salivary IgA proved to be the stronger of the two predictors.

A sign of overtraining?

Thus, if resources permit, it does not seem to be an unreasonable idea to monitor athletes’ salivary IgA levels over the course of a training year. If these levels dip, it could be a sign that the athlete is overtraining and needs lighter workouts for a while, at least from the standpoint of immune-system competency. True, immune-system competency and performance potential may not necessarily peak or trough simultaneously, but it is very clear that an athlete is more susceptible to infections when immune-system function declines, and infections can produce major setbacks in an athlete’s overall training.

Note, however, that salivary IgA, like most physiological and psychological variables, may follow a circadian rhythm, cresting and ebbing over the course of a day. If this is true, it might set up a situation in which one particular time of day would be the worst time for strenuous training from the standpoint of maintaining immunocompetency. For example, if salivary IgA levels reach their naturally lowest point at 1600 hours, severe workouts carried out at that time might produce the greatest-possible plummets in IgA, increasing the risk of infection significantly, compared with exercising when IgA concentrations are fairly high.

Larkish or owlish

To examine such possibilities, researchers in the Department of Sport Sciences at Brunel University in Middlesex and in the Department of Sport and Exercise Science at the University of Luton carefully studied 14 healthy, male competitive swimmers who normally trained for 90 to 120 minutes in both the morning and evening(2). These swimmers had an average age of 19, weighed about 71 kilos (156 pounds) each, and had been training for a mean of nine years, with an average total swimming distance of 21.3 kilometres per week. Two of the swimmers were club standard, one was county standard, two were regional standard, and nine competed at the national-standard level. Initial assessment of their ‘circadian chronotype characteristics’, which tend to reveal whether individuals are ‘larks’ or ‘owls’ with regard to their daily vigour and overall activity, revealed that 11 of the athletes were intermediate (neither morning larkish nor evening owlish), two were moderate evening types, and one was a definite evening person.

In a completely randomised, cross-over design, each swimmer completed two tests at 0600 and 1800 hours in the same indoor heated pool, with a minimum time of 36 hours between test sessions. 0600 and 1800 hours happen to be the most common times for swim training in the UK and in parts of Europe, and there is also evidence that certain physiological variables may peak or reach a nadir at those two points in time (3 & 4). A strong feature of the study was that many of the variables known to produce changes in salivary IgA levels (as well as in the concentrations of another key chemical, cortisol, which was also studied) were tightly controlled. For example, the swimmers did not exercise intensely, take dietary supplements, or consume any medicine during the 24 hours before test sessions. In addition, sex, tobacco use, alcohol consumption, and caffeine intake were restricted for 12 hours before exercise, and eating was banished for eight hours prior to exertion. Even drinking water, brushing teeth, and chewing gum or mints were prohibited during the final hour before swimming.

What the test involved

Prior to a test, a series of flexibility exercises and a 600-metre warm-up at each athlete’s preferred pace were completed. In addition, two 100-metre repetitions of front-crawl swimming were carried out at the average split time of a 400-metre target time to familiarise each swimmer with target pace. The test itself consisted of five 400-metre reps using the front-crawl swimming style, performed at a velocity which was 85% as fast as the season’s best time, with a one-minute recovery between each 400m. At the end of each 400, the subjects recorded ratings of perceived exertion (RPE) using a 0-10 Borg Scale, and after the fifth rep the swimmers quickly exited the pool and had the quality of their saliva evaluated. The athletes’ moods were monitored before and after the tests using a Profile of Mood States (POMS) questionnaire (mood may alter IgA concentrations).

The results

As it turned out, IgA did follow a pronounced circadian rhythm, with low levels of IgA secretion observed in the morning and significantly higher rates of secretion occurring in the late afternoon. The overall ‘flow rate’ of saliva was also greater at 1800 hours, compared with 0600. In contrast, levels of cortisol – a hormone known to compromise immunocompetency – were higher in the morning and slack in the evening. Although cortisol tends to hamper the immune system, it does promote gluconeogenesis (the formation of glucose within the body via the utilisation of proteins and fats) and also stimulates appetite, explaining why it tends to be elevated during the morning. In addition, the 400-metre reps significantly boosted cortisol levels in the swimmers’ saliva.

What does this mean to you as an athlete? Basically, the data from the Brunel-Luton research suggest that the optimal time for training from the standpoint of health (i.e., the time of day associated with the least suppressive effect on the immune system) would have to be the evening (around 1800 hours). The reason for this is that cortisol levels are low at this time, while the flow rate of saliva is high and the secretory rate of IgA is also elevated, both before and after workouts.

The perils of xerostomia

Although it seems innocuous on the surface, overall salivary flow rate is one of the body’s key defences against disease; in fact, some health experts believe it may be the most influential factor with regard to protection against oral pathogens and infections(5). Interestingly enough, individuals suffering from xerostomia (dry-mouth syndrome) have a much-larger risk of oral infections and the presence of pathogenic bacteria in their mouth cavities, compared to people with normal mouths. Thus, the decreases in overall salivary flow as well as in the rate of secretion of IgA at around 0600 makes early morning appear to be a relatively risky time to train, from the standpoint of maintaining good health. Many athletes will of course rebel at the thought of doing away with their early-morning training sessions and will argue – quite rightly – that these workouts don’t automatically make you ill: they may simply increase your chances of becoming so. Athletes who work out two or more times a day will be particularly reluctant to throw away their morning activity, especially since an early-morning session is often one in which an athlete feels freshest and is best able to carry out really high-quality work. However, athletes who have recurrent infections or who have suffered from infections at very inopportune times (before very important competitions, for example), may need to take special heed of the new evidence. Such athletes might want to decrease their frequency of morning workouts, especially prior to major competitions or during the recovery from illness or injury. Individuals who are training at altitude might need to be particularly careful, since altitude itself can induce a certain amount of immunosuppression. Note, too, that the research and related topics should remind all athletes of the need to remain well-hydrated. Dehydration reduces overall salivary flow rate, which happens to be one of the body’s key defences against disease. The traditional admonition to drink eight to 12 glasses of water per day might annoyingly keep you peeing, but it also may keep you healthily and productively performing.

Jim Bledsoe

References

‘Salivary IgA Levels and Infection Risk in Elite Swimmers’, Medicine and Science in Sports and Exercise, Vol 31 (1), pp67-73, 1999
‘Circadian Effects on the Acute Responses of Salivary Cortisol and IgA in Well Trained Swimmers’, British Journal of Sports Medicine, Vol 36, pp260-264, 2002
‘Interactions between Sleep, Other Body Rhythms, Immune Responses, and Exercise’, Canadian Journal of Applied Physiology, Vol 22, pp95-116, 1997
‘Circadian Changes in the Secretory Activity of Nasal Mucosa’, Acta Otolaryngology, Vol 106, pp281-285, 1988
‘The Effects of High-Intensity Intermittent Exercise on Saliva IgA, Total Protein and a-Amylase’, Journal of Sports Science, Vol 17, pp1-6, 1999