Evaluation of the Sensory Perception of Sweet Taste in People with Diabetes Mellitus Type 1 in Indian Population: A Comparative Study

The physiology of taste perseverance involves induction of taste receptors by tastant stimuli on threshold stimulates gustatory nerve endings of tastes receptors causing a taste feeling (Gutierrez and Simon 2011) The taste threshold can be altered in several conditions along with genetic factors (Keskitalo et al., 2007), age (Seiberling and Conley 2004), body weight (Yanina Pepino et al., 2010), consumption of alcohol (Kampov-Polevoy et al., 2001), smoking (Pepino and Mennella 2007), acute and chronic diseases (Bloomfeld et al., 1999) and surgical interventions (Mori et al., 2019).

Taste impairment is not considered a serious handicap and diabetic patients are not systemically screened for taste disorders. Taste disorders can lead to modify food intake & can influence the metabolic control. Decrease in sweet taste sensitivity can lead to greater consumption of sugar which might be a factor driving already diabetic patients to overt Diabetes (De Carli et al., 2018). Hence, it is important to research the taste sensitivity among diabetic population.

An increased state of taste threshold is related to increased blood glucose levels (Wasalathanthri et al., 2014) leading to a dampened response to sweet in type 2 diabetics (Gondivkar et al., 2009).

Till date, there have been numerous studies done on the sweet taste sensitivity in Type 2 diabetes mellitus patients (Kumari and Kumar, 2020), (Pugnaloni et al., 2020), (Tjahajawati et al., 2020), (Takai and Shigemura, 2020) No studies have been conducted on the taste impairment on Type 1 diabetic patients. Hence, our study aimed to compare the taste threshold of type 1 diabetics with non-diabetics and also to assess whether sensitivity for sweet taste is altered in type 1 diabetics when compared with non-diabetics.

MATERIALS AND METHODS

Subjects:

The study design was cross-sectional with a convenience sample conducted in the Endocrinology Outpatient department at Osmania General Hospital, Hyderabad. This study consisted of 200 subjects involving both males and females, aged 20 to 45 years old, grouped into 2: control and test. The control group consisted of 100 non-diabetic individuals and the test group had 100 patients diagnosed with type 1Diabetes Mellitus, who were willing to participate in the study. Exclusion criteria included subjects who consumed alcohol in last 24hrs, older patients and smoking, pregnant and lactating females and type 2 diabetes. Data collection was conducted from November 2014 to October 2016. Our study was conducted after an approval from ethics review committee from the university. All the subjects were included only after a written informed consent from them

Preparation of different concentrations of glucose solutions:

1M is 180g of glucose in 1litre. 100ml glucose solutions were prepared at six different concentrations and were collected in a container having a dropper. Every time fresh solutions were prepared on the testing day. (Table 1)

Procedure:

All the participants were informed to arrive at the study site at around 8am to 8:30 am on the day of test. The subjects were instructed not to take anything orally except water before one hour of the testing. The investigator distributed questionnaire to receive an information about the demographic details of subjects, food intake (sugar consumption), previous medical history and medication history. The patients were assessed for height and weight. The entire procedure of the test was explained to the subjects before starting the test. The test for taste perception was completed before 11am in a complete a fragrance -free room and was completed Testing started with minimum concentration of glucose solution. Two to three drops of solution were given at the middle of the dorsum of the tongue approximately 1.5 cm from the tip.

Subjects were asked whether he/she was able to feel any taste sensation and was asked to indicate taste quality. If the subjects could not feel the taste sensation then a solution of next higher concentration was tested. In between the different concentrations distilled water was used for rinsing. Whenever the subject felt the sweet taste that concentration was noted.

Statistical methods:

Concentration at which sweet taste is perceived was considered as Primary outcome variable.

Study group (Diabetic v/s Non-Diabetic) was considered as primary explanatory variable.

Age and Gender were considered as other explanatory variables. The data was analyzed for normal distribution in each group of variables and was anlaysed by histograms and Q-Q plots.for normal distributed data Shapiro- Wilk test was applied. Chi square test was used to analyze categorical outcomes. P value < 0.05 was considered statistically significant. IBM SPSS version 22 was used for statistical analysis.(Owen et al., 2016)

RESULTS

A total of 200 subjects considered into final analysis. Among the study population, 100 (50%) participants belonged to Diabetic Group and 100 (50%) participants belonged to Non- Diabetic Group. (Table 2)

Comparison of demographic parameters between study groups (N=200) was done and there was no statistically significant difference between two groups in baseline parameters like age (P value 0.086) and gender (P value 0.154). (Table 3)

Among the study population, majority of participants had 0.25M (51 (51%) in non-diabetic and 28 (28%) in diabetic), 0.50M (26 (26%) in non-diabetic and 37 (37%) in diabetic) and 1M (11 (11%) in non-diabetic and 23 (23%) in diabetic) as concentration at which sweet taste is perceived. (Table 4)

Table 1: Amount of glucose at different molar concentrations

Concentrations	Amount of glucose in 100ml of distilled water
0.0625M	1.125g
0.125M	2.25g
0.25M	4.5g
0.5M	9g
1M	18g
2M	36g

Table 2: Descriptive analysis of Study Groups in study population (N=200):

Study Group	Frequency	Percentage
Diabetic	100	50%
Non-Diabetic	100	50%

Table 3: Comparison of demographic parameters between study groups (N=200):

Parameter	Study Group		Chi-Square	P-Value
	Diabetic (N=100)	Non-Diabetic (N=100)
Age groups
<=30	36 (36%)	48 (48%)	2.956	0.086
>30	64 (64%)	52 (52%)
Gender
Male	61 (61%)	51 (51%)	2.029	0.154
Female	39 (39%)	49 (49%)

Table 4: Comparison of Concentration at which sweet taste is perceived between study groups (N=200):

Concentration at which sweet taste is perceived	Study Group		Chi-Square	P-Value
	Diabetic (N=100)	Non-Diabetic (N=100)
0.0625M	0 (0%)	6 (6%)	*	*
0.125M	4 (4%)	6 (6%)
0.25M	28 (28%)	51 (51%)
0.50M	37 (37%)	26 (26%)
1M	23 (23%)	11 (11%)
2M	8 (8%)	0 (0%)

*No statistical test was applied due to 0 value in one of the cells

DISCUSSION

Diabetes is a major health care problem in India with an estimated 66.8 million people suffering from the condition, who represent the largest number of any country in the world (Joshi 2015). A vast majority of the individuals are unaware/undiagnosed of their ailment status are left untreated and pose complications at end stage of the disease. Hence, it is very necessary to detect this category of undiagnosed individuals early and provide necessary treatment (Mohan et al. 2007).

Very few studies have studied the taste perception in type 1 diabetes in comparison to normal individuals. Hence, we aimed to access and compare the taste threshold in type 1 diabetics with normoglycemic individuals.

Here, the mouth threshold index technique was effective in assessing the taste sensitivity in Type 1 diabetic patients as our study found lower thresholds to perceive the taste of sweet in controls compared to type 1 diabetics. These results substantiated with the only study that recorded the taste threshold in Indian population which was conducted by Khobragade et al (2012) where threshold of sucrose was used, as compared to our study where glucose was used.

Baseline characteristics of the subjects in the two groups are shown in Table 2. The con-founders on taste thresholders was presumed to be small as both the groups were adjusted for gender, age and other cofounders. For nearly 4 decades the impact of type 2 diabetes mellitus on taste sensitivity is well known.(De Carli et al. 2018, Wasalathanthri, et al., 2014,

Gondivkar et al. 2009, Tepper et al. 1996) The exact mechanism behind this is still obscure. However, it is presumed that a complication of diabetes, neuropathy interrupts the nerve signals with microangiopathy of taste buds causes low taste perception.(Bhandare et al., 2014) the other reason was said to be the increase in the sweet taste receptors (STRs) T1R2 transcript receptors found in the intestine after glucose infusion. (Young et al. 2013)

In these present one-of-a-kind studies, a substantial increase in the mean threshold for glucose was observed in Type 1 diabetics as compared to normal individuals. This result was in line with a study wherein, they used a serial of diluted glucose solutions to analyze the threshold in type 1 diabetic population (70 in test and 70 in controls). The diabetic study population showed a significant increase for sweet threshold and other tastes. (Tepper et al., 1996) From the previous study findings this study too found a dampened taste perseverance in diabetics. Further to add, a study by Ribeiro Dias et al. (2016), also found increased thresholds to detect sweet taste perception in diabetics. Interestingly a study by Wasalathanthri et al (2014) found decreased sweet taste perception in prediabetics compared to controls. In a previous research it was shown that diabetics desire for high carbohydrate foods especially when they are in poor glycemic control (Yu et al. 2013). But, according to our knowledge there is no reported data to confirm whether this desire actually drives the diabetics to use more sugar to improve the taste of their food. Studies need to be conducted on this aspect of the disease process.

Altered taste was present only during certain time and not throughout the day as confirmed by a study by Nikhil Bhnadare et al (2014) Rather than being an indicator of duration or complications of disease, it could be an indicator of fluctuations in blood sugar levels. Hence, this study was conducted at a specified time of 8am to 10am for all the patients so as to avoid the time variation in taste perception. Hence the threshold for taste increases in diabetics. So, individuals sensing an increased threshold for glucose can use this sign as an alarm for a suspected diagnosis of diabetes mellitus.

CONCLUSION

From this cross-sectional study, it is evident that individuals with Type I diabetes mellitus have a higher threshold index value for the sweet taste. This implies that Type 1 diabetics need higher glucose concentrations to recognize the sweetness of foods. This may contribute to an increase in sugar consumption and further worsening of the disease.

LIMITATIONS AND RECOMMENDATIONS

There were few unavoidable limitations in this study. Some being; a small sample size. The severity of the diabetics was not considered in this study through blood glucose levels and HbA1c levels. Medications (hypoglycemics or anti-hypertensives) also can cause taste perception alterations, which was not recorded in this study. Further investigations and better study designs including the above-mentioned limitations can be incorporated in future studies on this aspect of Type 1 diabetes.

ACKNOWLEDGMENTS

We acknowledge the technical support in data entry, analysis and manuscript editing by “Evidencian Research Associates”.

CONFLICT OF INTEREST

The authors declare no conflicts of interest.