The fluctuation of the salivary flow has been established via many studies but the times of fluctuation and the many factors that contribute towards it remain to be known. Saliva is an integral part of the oral cavity which helps to provide immunity to the body alongside other functions. This manner of fluctuation has been found to be close to the circadian rhythm. Cortisol as well as immunoglobulin A or IgA, are also very important components of the saliva, which help in providing immunity. The study is aimed to verify and ascertain the correlation of cortisol as well as IgA in the various cicardian rhythms.
Studies such as those of Dimitriou et al, have already shown a cicardian rhythmic effect of cortisol peaks and falls in his study carried out on fourteen healthy male swimmers, although most of the study was focused around the effect of exercise on the cortisol and IgA levels in the saliva (Dimitriou et al,2002, pp 260 and 262).
The article is aimed at looking at some articles that have researched the variations in the quantity of IgA and cortisol in the saliva based on circadian rhythms. These researches were very difficult to find, chiefly because there are very few authenticated researches carried out in the area. Most of the related researches have studied the changes in the salivary composition during exercise and the effects of stress on the salivary flow and composition. More research in this area is required. Till then a discussion based on the studies till now is presented.
The saliva has been found to be a very important indicator of various substances of the body. The salivary cortisol levels are almost equally correlated to the level of cortisol found in the blood. Along side, cortisol is also affected by the various physical states of the body such as exercise, and can aid in diagnosing cases of Cushing’s syndrome etc. The influence of time and day rhythms on its concentration however, remain to be known fully (Kaufman and Lamster, 2002, pp 202 and 208).
There are studies however, that do show the rise and the circadian pattern of cortisol in the body, in-dependant of any exercise. Cortisol levels in the saliva increase in the morning, which leads to an increase in the neutrophil count and helping in T lymphocyte function (Hamer et al, 2004, pp 639).
The same rise of cortisol levels in the morning have been documented by Wilhelm et al in 2007 (Wilhelm et al, 2007, pp 358 and 360). He carried out his study on 16 young men who were observed in both laboratory as well as home conditions. Many serum and salivary levels of substances were collected for two consecutive days. These included serum cortisol and ACTH levels and salivary cortisol levels. These levels were assessed at pre awakening and post awakening. The findings indicated that there was a steeper increase in the cortisol and ACTH levels upon waking. The researchers claimed that this phenomenon is not related to circadian rhythms but is due to the psycho-physiological process of sleep awakening transition (Wilhelm et al, 2007, pp 359 and 366).
The salivary IgA has been indicated to be found in decreased quantities when the person is stressed. This is therefore a very helpful tool in gauging the stress in a person. However, salivary IgA is also under influence of many other factors, and according to the stimulus, the rate of secretion can vary. (Skandakumar, 1995, pp 339 and 342) In contrast, Huckelbridge found that during acute stress phases, the person is likely to have a transient increase in the rate of salivary IgA, as opposed to a decrease in the chronic stressful states. His study showed that an increased spike level of both cortisol and IgA in the saliva after awaking showing a diurnal pattern of increase and decrease in the quantity. This increase shown in the early morning is followed by a decline following 6hours of waking. This quantity is again increased in the evening, then decreases at night and then picks up at around midnight (Hucklebridge et al, 1998).
Shirakawa et al in 2003 studied the secretory times of IgA and cortisol in various times of the day in young adults. The number of persons used in the study was 8 in number. They fond that the rates of secretion of IgA and cortisol fluctuated showing peak times or macrophases at 06:50 hours, 09:04 hours, and 19:01 hours respectively. the Mesor for salivary IgA was 0.30 mg/ml, for cortisol was 8.56 ng/ml and for flow rate was 0.47 ml/min respectively (Shiakawa et al, 2004, pp 115, 117). However, the IgA peak rate flows were not in line with the peak flow rates of the saliva. in fact, the nadir flow rates were found to be anti to each other for IgA and salivary flow rate. Shirakawa also found that the ratios of IgA to total proteins also vary significantly between different hours of the day, which can be as high as 1:3 in the mornings than compared to evening ratios. This concentration of IgA then again starts to rise in the midnight which may suggest a compensatory mechanism (Shiakawa et al, 2004, pp 115, 117).
The finding of Shirakawa’s research shows that IgA secretion is not simply dependant on the secretary patterns of saliva, but is under a separate influence. The researchers suggested that there is more likely to be a presence of the central circadian pacemaker, which influences the production of IgA (Shiakawa et al, 2004, pp 118, 120). Age is another important factor that influences the quantity of salivary IgA in a person. The salivary IgA concentration is less in ages below 7 years of age than in those who are above it (Kugler, Hess and Haaki, 1991).
IgA levels have been shown to increase in the saliva after any form of physical activity. Most of the studies have shown that an increase in the activity leads to an increase in the IgA levels in the saliva after exercise. This mechanism may also help in understanding the circadian rhythm related phenomena, where by awakening leads to consequent increase in the activity, thereby leading to an increase in the quantity of IgA in the saliva. The study by Sari-Saraf also showed that men showed an increase in the IgA levels after physical activity. (Sari-Saraf, 2003, pp 526 and 528)
Conclusion
The importance of studying the changes in the levels of various salivary components is the various effects that they have on the defense mechanism of the body. Any changes from the median may make the person vulnerable to infections in stages where the salivary cortisol and IgA levels are decreased. Also, these changes may be why their importance is manifested in children in the supplementation of IgA via the mother’s milk. The number of studies in this area is still very limited and there is still a lot to be learned about the various neuroendocrinological processes that govern such changes. However, salivary IgA and cortisol do show circadian patterns of high and low concentrations in the body.
References
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