Effect of HIIT (high-intensity interval training) on vulnerability to dental caries

Abstract

Objective

High intensity workout stimulates the sympathetic nervous system and causes changes in the salivary composition. We hypothesized that activity of caries-causing bacteria in saliva may differ before and after workout. The objective of the study was to investigate if there is any difference in the oral microbial activity before and after HIIT (High Intensity Interval Training) workout.

Methods

Unstimulated saliva was collected before and after HIIT workout (n = 35). The workout was performed until the participant's heart rate reached 70–80% of maximum heart rate. The microbial activity of saliva was estimated using Oratest.

Results

The participants belonged to 4 ethnities- Indian, Malays, Chinese and Others (18–22 years). The post-workout salivary microbial activity was higher than the pre-workout levels, being statistically significant (P = 0.010). The increase in the post-workout microbial activity among females was found to be higher when compared to males. We also found significant different according to the ethnicities.

Conclusion

We conclude that caries activity increases immediately after a vigorous workout and remains high at least for 15 min. Further studies are needed to validate the findings. Workout enthusiast should be aware of this so that they can take necessary precautions and be more regular with their dental check-ups.

Highlights

• •The microbial activity of saliva was found to be higher after high intensity interval training (HIIT).
• •The post HIIT rise in microbial activity was sharper among Female participants.
• •The post HIIT rise in microbial activity was sharpest among Chinese participants.

1. Introduction

Dental caries is a global public health problem and the most widespread noncommunicable disease. It may depreciate the quality of life due to pain and loss of teeth.¹ The etiology of dental caries is associated with oral microbial ecology.³ Exercise of various forms alters the oral microbial ecosystem by way of changing the composition of saliva and the amount of saliva.⁴

Many studies have shown that athletes, sportspersons, and individuals involved in extensive endurance training have a higher incidence of dental caries or dysbiotic oral microflora.5, 6, 7 An increasing number of people have become involved in endurance training and high intensities of exercises to improve their health and appearance. Hence, it is crucial to recognize the change in oral microbial activity during any workout among non-athletes. To confirm our hypothesis that the oral microbial activity may differ before and after workout, we investigated the changes in the oral microbial activity happening immediately after a high-intensity interval training (HIIT) among young adults who are not professional athletes. This paper presents the results of our preliminary work and discusses the changes in the microbial activity observed after HIIT in a young adult population, with some comparisons made among different ethnic groups and genders.

2. Methods

We hypothesized that the activity of caries-causing bacteria in saliva may differ before and after a vigorous workout. To investigate this, we selected HIIT workout, since this workout combines aerobic training with weight training and is intense enough to rapidly elevate the heart rate. Also, HIIT is one of the most popular workout form performed.⁸

In order to measure the caries activity, we selected Oratest, as the reliability of Oratest has been confirmed in many studies through comparison with other caries activity test and with the caries index of individuals.^9,10

Students from a pre-clinical phase of a medical college, who were willing to be a part of the study were included as study subjects. However, those students undergoing orthodontic treatment or having any other oral diseasess such as aphthous ulcers or gingivitis, those who could not perform HIIT workout for any reason, and those who were under any kind of medication in the past 1 week were excluded. Ethical clearance was obtained from the institutional ethics committee (IEC:202/2019). This study was also registered under Clinical Trial Registry, India (CTRI/2019/06/019694).

We provided a demonstration workout video to the participants a few days before the actual day of testing, to enable them to familiarize themselves with the workout. On the day of the trial, we briefed participants and obtained written informed consent from them.

3. Procedure

Unstimulated saliva was collected before and 15 min after the HIIT workout. The HIIT workout comprised of 45-sec workout followed by 15 s of rest for each exercise until their heart rate reaches 70% of their maximum heart rate. All participants performed the same workout. The heart rate was monitored using a pulse oximeter. The time and venue were kept constant for all participants.

Microbial activity of the collected saliva was assessed using Oratest. Apparatus required was screw-capped test tubes, sterile beakers, 10 ml disposable syringes, pipette, mirror, test tube stand and a stopwatch. The reagents required were 0.1% aqueous solution of methylene blue and sterilized milk at room temperature¹¹

The procedure of Oratest is described in Fig. 1. The time taken for the color change was recorded for pre-workout and post-workout samples. This is called Oratest score. Formation of a 10 mm ring seen through the glass place at the bottom of the test tube stand was considered the endpoint of color change. Statistical analysis.

Fig. 1.

Procedure for Oratest

Our alternate hypothesis was that the mean oratest scores of the participants before HIIT workout will not be the same as the mean oratest scores after HIIT workout. Paired sample t-test was used for hypothesis testing.

Additionally we also checked if the pre-workout and post-workout oratest scores were similar in both genders or not. Our second alternate hypothesis was that the mean pre and post workout scores among genders are not same. To test the hypothesis independent samples t-test was performed.

The data had a normal distribution and hence mean was chosen as a measure of central tendency. The level of significance was kept at P < 0.05, and confidence interval was taken as 95% for both tests.

4. Results

A total of 35 participants were included in the present study. Both genders were involved (Female = 62.9%, Male = 37.1%). There were mainly three ethnicities involved in the study, Chinese (48.6%), Malay (17.1%), and Indians (22.9%) and others (11.4%) (See Fig. 2 and Fig. 3).

Fig. 2.

Gender distribution of study population

Fig. 3.

Ethnicity distribution of study populartion

Comparison of mean oratest scores before and after the HIIT workout in the entire sample: The mean oratest scores before HIIT workout was found to be greater than the mean oratest scores after HIIT workout. The difference between the mean Oratest scores in pre-workout sample and post workout samples was found to be statistically significant (P = 0.010) (Table 1).

Table 1.

Mean scores of study participants obtained before and after HIIT with respect to gender and ethnicity.

		Before HIIT Mean ± SD	After HIIT Mean ± SD	t	df	.sig (2 tailed)	CI
Overall		216.6 ± 167.7	176.8 ± 125.3	2.7	34	P = 0.010*	10.1–69.3
Gender	Male	125.92 ± 131.12	116.8 ± 110.9	0.628	12	P = 0.542	22.4–40.58
	Female	270.18 ± 166.2	212.2 ± 121.9	2.7	21	P = 0.010*	14.6–101.19
Ethnicity	Malay	141.8 ± 88.1	115.8 ± 69.9	0.901	5	P = 0.409	48.1–100.1
	Chinese	284.6 ± 168.6	222.5 ± 129.3	2.7	16	P = 0.013*	14.7–101.3
	Indian	132.3 ± 159.8	148.2 ± 142.7	−0.817	7	P = 0.414	61.8–30.05
	Others	208 ± 195.6	131 ± 91.3	1.5	3	P = 0.227	84.7–238.7

Level of Significance at P < 0.05.

SD - Standard Deviation.

^aStatistically Significant.

Comparison of mean oratest scores before and after the HIIT workout in males and females: Both genders revealed a drop in oratest scored after HIIT workout. However the difference was not statistically significant in males. The difference in mean Oratest scores post-workout among females was found to be statistically significant (P = 0.010) (Table 1).

Comparison of mean oratest scores before and after the HIIT workout in different ethnicities: There was a reduction in mean oratest scores after HIIT workout among Chinese, Malays and ethnicities characterized as others. However, there was an increase in the mean oratest scores after HIIT workout among Indians. The difference in mean Oratest score among only Chinese participants statistically significant (P = 0.013). (Table 1).

Comparison of Pre- HIIT oratest scores between genders: The mean pre-workout Oratest scores of females was higher than that of males and this difference was statistically significant (P = 0.012) (Table 2).

Table 2.

Comparison of mean scores before and after HIIT between genders.

Groups	Gender	Mean ± SD	t	P- Value	CI
Before HIIT	Male	125.92 ± 131.12	2.6	P = 0.012*	254.1 to −34.3
	Female	270.18 ± 166.2
After HIIT	Male	116.8 ± 110.9	2.3	P = 0.027*	179.4 to −11.3
	Female	212.2 ± 121.9

Level of significance at P < 0.05.

^aStatistically significant.

SD= Standard Deviation.

Comparison of Post- HIIT oratest scores between genders: The mean post-HIIT Oratest scores of females was higher than that of males and this difference was statistically significant (P = 0.027) (Table 2).

5. Discussion

The activation of the sympathetic nervous system during a vigorous workout causes some changes in the salivary composition¹² and hence we hypothesized that it could possibly alter the oral microbial activity as well.

Dental caries is majorly associated with Streptococcus mutans, Lactobacilli and Actinomyces.¹³ Thus, we selected Oratest as a tool for assessment of the oral microbial activity. Oratest was developed by Rosenberg et al., in 1989. It is a chairside caries activity test which is also non-invasive and economical. The Oratest is based on the concept of oxygen depletion by the aerobic bacteria in expectorated milk samples. In the normal state, aerobic dehydrogenase, the bacterial enzyme, transfers protons and electrons to oxygen. When oxygen is being utilized by the aerobic bacteria, methylene blue (blue in color) mixed in the expectorated milk serves as an electron acceptor, which in turn is reduced to leucomethylene blue (colorless). Therefore, the metabolic activity of the aerobic bacteria can be demonstrated with the reduction of methylene blue. Rinsing with the milk dislodges the microorganisms in the oral cavity and acts as a substrate for their metabolic activity. The white color of the milk allows the easy detection of the formation of leucomethylene blue, an appearance of a white ring at the bottom of the test tube. This surmises that the lesser the time is taken for the ‘white ring’ to appear, the higher the microbial activity in the oral cavity.¹⁴ Reliability of Oratest has been confirmed in many studies through comparison with other caries activity test and with the caries index of individuals^9,10,15

HIIT has become popular for improving variables related to endurance performance among multiple populations, including adult endurance athletes. HIIT has become popular for improving endurance in athletes, sedentary adults and among those with some cardiovascular diseases.⁸

To test our hypothesis that HIIT can alter oral microbial activity, we conducted a pilot study with 35 participants. Most participants were females. Also, the study participants belonged to one of the three ethnicities- Indians, Chinese and Malays. Among the three ethnicities majority were Chinese, followed by Indians and Malays.

The autonomic nervous system controls salivary secretion. The quality and quantity of saliva vary depending upon whether the stimulation is sympathetic or parasympathetic. High-intensity workout activates the sympathetic nervous system, which reduces the flow of saliva and increases its viscosity. This change is saliva can also be attributed to systemic dehydration and mouth breathing. Several studies have reported a correlation between low salivary flow rate and high caries incidence. However, in the present study, we did not assess the salivary flow rate.^6,16

The mean Oratest score before workout was found to be 216.6 ± 167.7 min whereas the mean Oratest score after workout was 176.8 ± 125.3 min. The difference between the mean Oratest scores before and after HIIT was statistically significant (P = 0.010). As explained earlier, the lesser the Oratest score the higher the microbial activity. This indicates that the microbial activity is significantly increased after HIIT workout.¹⁷

In our gender-wise analysis, the mean difference Oratest score before and after HIIT workout reduced in both males and females. However this reduction was statistically significant among females. This means that the microbial activity increases more markedly among females after HIIT workout when compared to males. Additionally, both pre and post workout Oratest scores were higher among females than in males indicating that the baseline microbial activity is lower among females. This is a contradiction with most epidemiological surveys that reveal females being more susceptible to dental caries.^2,18 The reasons for this gender-based rise in microbial activity after a workout can be explored by further studies.

The difference in mean Oratest score was found to be more marked among Chinese participants, than other ethnic groups. This difference between ethnicities was also statistically significant (P = 0.013). Even though there was an increase in the microbial activity among Malays and other ethnicities, Indians showed an opposite trend. Congshi Shi et al. have reported significant ethnic disparities in oral health even after adjusting for demographic, socioeconomic, and caries-related behavioral factors.³ Drummond et al. have also reported ethnic differences in oral health-related conditions; however, in their work, the discrepancies have been attributed to education and income.² In the present study, however, education and income cannot be attributed to ethnic differences, and further investigation is needed to explore the reasons for the same.

This was a pilot study to explore the relationship between microbial activity and HIIT if any. And hence the sample size of the study was very low. Also, there was no control group. With the results obtained from this pilot study, another study with a control group and higher sample size is underway.

The present study was taken up as an exploratory preliminary study and hence had a relatively small sample size of 35 and no subgroups. A study with larger sample size and the more specific microbial test could zoom into further details along with this research work. The results of the present study open the scope of a plethora of research work that could be performed on the effect of different workout regimens and post workout drinks on the caries activity of oral cavity, the best post-workout drink or best time to have the post workout drink in the context of oral health. The present research work provides scientific evidence of an increase in microbial activity after High-Intensity Interval Training (HIIT), and all fitness enthusiasts must be aware of this. This can enable them to make better choices about their post-workout drinks. For the same reason, all individuals performing HIIT on a regular basis should be more diligent with their routine dental check-ups.