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Abstract

Objectives: Assess the relationship between lifestyle and oral health-related quality-of-life (OHRQoL) of residents in a blue zone, Loma Linda. Methods: A cross-sectional study was conducted using a questionnaire including demographics, lifestyle, and Oral Health Impact Profile (OHIP-14). Lifestyle cumulative scores ranged from 8-32, lower scores indicating greater conformity to Power 9® lifestyle, characterized by observing Sabbath, time with friends, volunteering, exercising, eating lots of plants, eating meat in moderation, drinking a lot of water, snacking on nuts, and eating an early dinner. OHIP-14 assessed OHRQoL, with scores from 0-56. Negative binomial regression was used, with significance of alpha = 0.05. Results: A total of 350 surveys were collected. Cumulative lifestyle showed a mean of 13.9. Spending time with friends was the most adhered to activity (96%) while the least followed was having early dinners (71.2%). Asians (Mean = 14.2) had significantly higher lifestyle scores than Whites (Mean = 13.7). The mean OHIP-14 was 7.01. Whites had lower OHIP-14 scores than Asians, indicating better OHRQoL. Race, nut consumption and exercise were significant predictors for increased OHRQoL (P < 0.05, in all instances). Conclusions: Loma Linda residents adhere well to the Power 9® lifestyle. There are significant predictors such as nut consumption and exercise for increased OHRQoL.

Keywords

lifestyle blue zone oral health-related quality-of-life oral health impact profile

“Our study findings highlighted a notable difference in adhering to positive lifestyle patterns and OHRQoL between Whites and Asians living in a blue zone.”

Introduction

Blue Zones are areas scattered across the globe where people consistently exceed conventional lifespan expectations, often surpassing the centenarian mark. These rare locations include Okinawa, a pacific island situated at the southernmost of Japan, Ikaria, a mountainous Greek island located in the Eastern Aegean Sea, Sardinia, a mountainous terrain that is located along the western coast of Italy in the Mediterranean Sea, Nicoya, a northwestern region of Costa Rica located along the Pacific Ocean, and lastly, Loma Linda, a Southern Californian city in the United States, which is predominantly inhabited by Seventh-Day Adventists.^1,2 Researchers, including Dan Buettner, have focused on understanding the secrets behind their unique longevity and seeing whether these traits can be adopted by the general population. Buettner and his team unveiled the “Power 9®,” a compilation of evidence-based lifestyle habits common across these zones. According to the concept, Blue Zone residents have a clear sense of purpose, are physically active, manage stress effectively, and practice dietary moderation. Residents typically prioritize plant-based diets or minimal meat consumption and often enjoy wine in moderation, supported by religious and family values that create strong social networks essential for holistic well-being.³

In contrast to their remote counterparts, Loma Linda is an urban city situated in San Bernardino County, California, USA, with a population of around 25,000 as per the 2020 census.⁴ Nearly one-third of Loma Linda’s residents are Adventists, who embrace a lifestyle characterized by wholesome nutrition, ample rest, regular exercise, and abstinence from deleterious substances like alcohol, tobacco, and narcotics, all founded by a steadfast devotion to faith and hope to give meaning to life.⁵ Numerous studies have linked the Adventist lifestyle to longevity and health.^5-8 One study highlighted that Adventist students were more likely to follow healthier lifestyle behaviors compared to non-Adventist students, and that these behaviors were strongly linked to lower obesity risk and reduced risky eating patterns.⁵ Notably, vegan diets, were associated with decreased risk of cardiovascular diseases, obesity, hypertension, type-2 diabetes, and certain types of mortality.⁶ Moreover, adopting healthy eating habits could help effectively prevent long-term weight gain.⁷ Additionally, vegetarian diets showed significant benefits in reducing mortality related to cardiovascular conditions, non-cancer diseases, renal issues, and endocrine disorders.⁸ Despite the existing literature on the relationship between lifestyle and health, there remains a lack of exploring the relationship between lifestyle patterns and oral health.

Hence, to assess the relationship between lifestyle and oral health the short version Oral Health Impact Profile (OHIP-14) was used in this study. OHIP-14 is a widely used tool to assess the impact of oral problems on the perceived quality of life of individuals.^9-12 The OHIP-14 questionnaire is composed of 14 questions that each address a specific facet of oral health and its impact on an individual’s daily life. Responses are scored and summed to provide an overall measure of oral health’s impact on quality of life, with higher scores indicating a more significant negative effect.¹³

The objective of the study was to assess the relationship between lifestyle patterns and oral health related quality of life in the Blue Zone of Loma Linda. We aimed to determine how participants living in this Blue Zone adhere to the “Power 9®” characteristics relevant to Loma Linda. We hypothesized that most participants would adhere to a lifestyle pattern unique to Loma Linda. Furthermore, we sought to examine the link between these lifestyle traits and oral health related quality of life. We hypothesized that there would be predictors related to oral health related quality of life.

Methods

Cross-Sectional Study Design and Sample Size Calculation

The study involving adults aged 18 years and above residing in Loma Linda, California, was conducted upon the approval by the Loma Linda University Institutional Review Board (IRB #5230470). Prospective participants were approached by a member of the research team at venues including Loma Linda University School of Dentistry as well as through outreach efforts at local churches and community centers. Participation involved the completion of a survey, with participants having the liberty to proceed at their own pace and not respond to all inquiries. As a token of appreciation, participants received a complimentary pen upon completing their involvement in the study.

The questionnaire used in this study was developed by integrating questions from a previously validated OHIP-14 questionnaire⁹ and others specifically designed for this research. Consisting of 28 items, the questionnaire was structured into 3 sections. Previous research suggested that a sample size of 130 in each group would be necessary to find a 35% difference in cumulative OHIP-14 score between Whites and Asians for 80% statistical power.¹⁴

Section I. Demographics

Demographics included residency in Loma Linda, age, gender, education level, race (categorized as White, African, Asian, Indian, and Hawaiian), and ethnicity.

Section II. Power 9® Lifestyle

This section of the questionnaire covered level of adherence to the Power 9®. These dimensions included adherence to Sabbath observance, regular exercise, social engagement, nut consumption, volunteering activities, dinner timing, vegetarian diets, and water intake. Lifestyle adherence was assessed with a focus on nut consumption and exercise. Participants rated their adherence on a 4-point Likert scale, ranging from 1 (strong adherence) to 4 (poor adherence). The cumulative score for lifestyle adherence ranged from 8 to 32, with lower scores indicating greater conformity to the Power 9®.

Section III. OHIP-14

To assess Oral Health Related Quality of Life (OHRQoL), the study utilized OHIP-14, which addresses functional limitations, physical pain, psychological discomfort, physical disability, psychological disability, social disability, and other handicaps. The severity of OHRQoL impacts was quantified by calculating a cumulative OHIP-14 score, ranging from 0 to 56. Higher OHIP-14 scores indicating worse OHRQoL, while lower OHIP-14 scores indicating better OHRQoL. Specific oral health indicators, including difficulties in pronouncing words, experiencing pain, feeling self-conscious, tense, embarrassed, irritable, and general health status, were measured and included as predictors in the model.

Data Analysis

The findings of descriptive analyses for cumulative score for lifestyle and OHIP-14 score, were reported as Mean ± SD. One-way analysis of variance (ANOVA) followed by Tukey HSD post-hoc test was used to test differences in OHIP scores by race. A Negative Binomial regression model was used to analyze the relationship between OHIP-14 scores (dependent variable) and the predictors, including race, lifestyle factors (nut consumption and exercise), and oral health indicators. This model was selected due to the overdispersed nature of the OHIP-14 scores. The log link function was used, and the model fit was assessed using the Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), deviance, and Pseudo R-squared. Model diagnostics were performed to check for overdispersion and multicollinearity among predictors. We used several R (v4.4.1) and Python (v3.12) packages for data analysis and visualization.¹⁵ The R packages “MASS” and “car” were employed to fit the Negative Binomial regression model and perform diagnostic checks, respectively. Data manipulation was conducted using “dplyr,” while visualizations were created using “ggplot2.” Model performance and selection criteria were assessed using the “performance” and “AICcmodavg” packages.

In Python, the “pandas” library was utilized for data preparation, and “statsmodels” was used for regression analysis. Visualizations were generated using “matplotlib” and “seaborn,” and additional statistical tests and diagnostics were conducted using “scipy” and “sklearn.”

Results

Descriptive Analysis

A total of 350 surveys were collected, with 20 ineligibles due to non-residency in Loma Linda and 10 exhibiting incomplete responses, with over 50% of questions unanswered. Ultimately, 320 participants residing within Loma Linda were included in the study. Participants’ age ranged from 18 to 88 years (Mean = 51.51, Standard deviation (SD) = 19.70). Gender distribution indicated that 60% were female, with the remaining being male or other. With respect to education, the majority of participants reported completing higher education (94.7%). Whites and Asians were the predominant racial groups within the participants, making up 48.6% and 45.3%, respectively.

Power 9® Lifestyle

The cumulative lifestyle score was measured by the overall sum of “Power 9®” adherence and ranged from 8 to 24 (Mean = 13.9, SD = 3.6). Figure 1 illustrates how participant adherence to these lifestyle habits varied, from strongly agree to strongly disagree within each item. Among the “Power 9®” lifestyle items, spending time with friends was the most adhered to activity, with 96% of participant engagement. Following closely, 90.3% of participants frequently ate plant-based foods, and 88.8% reported high water consumption. Conversely, the least followed habits were eating an early dinner (71.2%) and snacking on nuts (75.3%).

Figure 1.

Bar Graphs of Adherence to “Power 9®” Lifestyle.

OHIP-14

The cumulative OHIP-14 scores ranged from 0 to 42, with a mean of 7.01 and an SD of 7.36. Table 1 summarizes the mean score for each of the 7 OHIP domains, by race. There was a statistically significant difference in cumulative OHIP-14 scores between Whites and Asians (P = 0.002), indicating that oral health related quality of life was less adversely affected in Whites. Specifically, significant differences were found between Whites and Asians in the domains of functional limitation in pronouncing words and sense of taste as well as physical disability related to unsatisfactory diet and interruption of meals due to oral issues. Figure 2’s violin plot illustrates variations in score distributions between groups categorized as Whites, Asians, and Others. The White group displayed a unimodal distribution with a long upper tail, indicating a predominance of lower OHIP-14 scores but with some instances of higher scores. In contrast, the Asian group exhibited a bimodal distribution, suggesting 2 common OHIP-14 score levels: 1 lower and 1 mid-range. The Others group distribution mirrored that of the Whites, albeit with a shorter upper tail, suggesting fewer instances of higher OHIP-14 scores. The median scores, marked by the red dashed line within each violin plot, were lowest for Whites and highest for Asians. This visualization suggests potential disparities in oral health related quality of life across different racial groups.

Table 1.

OHIP-14 Scores (Mean/SD) by Domain and by Race.

OHIP Domains	Whites (N = 151)	Asians (N = 141)	Others (N = 28)	P-value	95% Confidence Interval (White vs Asian)
Functional limitation	0.27/0.61^*	0.53/0.75^†	0.36/0.59^*^†	0.005	Diff = 0.2600, 95CI = 0.0742 to 0.4458, P = 0.0031
Physical pain	0.64/0.80	0.77/0.81	0.79/0.76	0.330	Diff = 0.1300, 95%CI = −0.0909 to 0.3509, P = 0.3496
Psychological discomfort	0.70/0.95	0.94/0.99	0.82/1.10	0.115	Diff = 0.2400, 95%CI = −0.0306 to 0.5106, P = 0.0938
Physical disability	0.30/0.62^*	0.60/0.75^†	0.32/0.64^*^†	<0.001	Diff = 0.3000, 95%CI = 0.1120 to 0.4880, P = 0.0006
Psychological disability	0.45/0.76	0.65/0.79	0.29/0.62	0.020	Diff = 0.2000, 95%CI = −0.0103 to 0.4103, P = 0.0662
Social disability	0.26/0.57	0.38/0.67	0.13/0.38	0.070	Diff = 0.1200, 95%CI = −0.0464 to 0.2864, P = 0.2076
Handicap	0.26/0.57	0.42/0.64	0.23/0.54	0.051	Diff = 0.1600, 95%CI = −0.0053 to 0.3253, P = 0.0602
Cumulative OHIP score	5.74/7.36^*	8.59/7.42^†	5.86/5.48^*^†	0.002	Diff = 2.9000, 95%CI = 0.8990 to 4.9010, P = 0.0021

Different superscript letters (e.g., *, †) indicate statistically significant differences between groups after Tukey HSD Post-hoc test.

Figure 2.

Violin Plots of Distribution of Cumulative OHIP-14 by Race.

Negative Binomial Regression

The Negative Binomial regression model demonstrated good fit, with an AIC of 1438.304, BIC of 1511.299, and a Pseudo R-squared of 0.758. The model accounted for a significant portion of the variance in OHIP-14 scores, while also minimizing overfitting by focusing on the most relevant predictors. The results of main predictors (race, nut consumption, and exercise) with their respective regression coefficients, significance levels, confidence intervals, and effect sizes are summarized in Table 2. Asians had significantly higher OHIP-14 scores compared to Whites. This suggests that being Asian is associated with a 24.2% increase in the expected OHIP-14 score, indicating worse OHRQoL. No significant differences were found for other racial comparisons (African, Indian, Hawaiian vs White). Higher levels of nut consumption were marginally associated with better OHRQoL. Higher levels of exercise were associated with significantly lower OHIP-14 scores, indicating a protective effect of exercise on OHRQoL.

Table 2.

Negative Binomial Regression Model and Outcomes of Predictors.

Predictor	Coefficient (β)	Standard Error (SE)	P-value	95% Confidence Interval	Exp (B)
Race (Asian vs White)	0.217	0.065	<0.001	[0.092,0.337]	1.242
Nut consumption	0.293	0.126	0.020	[0.049, 0.537]	1.341
Exercise	−0.861	0.259	<0.001	[-1.370, −0.352]	0.423

Model Fit – AIC: 1438.304; BIC: 1511.299; Pseudo R-squared: 0.758.

The list predictors of OHIP-14 scores, including their coefficients, standard errors, P-values, confidence intervals, and their effect size are summarized in Table 3. Increased difficulty in pronouncing words, pain, feeling self-conscious, tense, embarrassed, or irritable, as well as poor general health, were all associated with significant increases in OHIP-14 scores. Specifically, pronouncing words was linked to a 27.0% rise in scores, while pain resulted in the highest increase at 44.6%. Feelings of self-consciousness, tension, embarrassment, and irritability led to increases of 15.9%, 26.8%, 22.2%, and 25.3%, respectively. Additionally, poor general health contributed to a 19.7% rise in OHIP-14 scores.

Table 3.

Summary of Significant Predictors of OHIP-14 Scores.

Predictor	Coefficient (β)	Standard Error (SE)	P-value	95% Confidence Interval	Exp (B)
Pronouncing words	0.239	0.040	<0.001	[0.160, 0.318]	1.270
Painful	0.369	0.040	<0.001	[0.290, 0.448]	1.446
Self-consciousness	0.148	0.037	<0.001	[0.075, 0.221]	1.159
Tense	0.237	0.050	<0.001	[0.139, 0.335]	1.268
Embarrassed	0.200	0.047	<0.001	[0.108, 0.292]	1.222
Irritable	0.225	0.046	<0.001	[0.134, 0.316]	1.253
General health	0.180	0.053	<0.001	[0.076, 0.284]	1.197

Model Diagnostics

The model was well-fitted, as indicated by a Chi-squared/DF ratio of 0.967, which suggests that the model appropriately accounted for overdispersion. Residual analysis showed no significant deviations from the model’s assumptions, and multicollinearity among predictors was not problematic, ensuring the robustness of the model.

Limitations of the Model

Despite the strong fit, the model’s complexity could still pose risks of overfitting, particularly with the inclusion of multiple predictors. Simplifying the model by focusing on the most significant predictors can further reduce this risk while maintaining explanatory power.

Discussion

Scientists are hard at work trying to understand what causes aging and exploring strategies to extend human lifespan, often looking to the characteristics of blue zone residents for inspiration. While studies have identified evidence-based lifestyle patterns unique to these areas, few have assessed residents’ adherence to these patterns. Our study is the first to evaluate the adherence of urban blue zone residents to these lifestyles and their correlation with oral health related quality of life. We found remarkably high adherence to positive lifestyle patterns. Out of ten residents 9 adhered well to activities such as “spending time with friends” and “volunteering” which appears crucial in fostering community connection and preventing isolation. This social aspect may indeed play a vital role in promoting a healthy, long life—a notion supported by research indicating that the presence of family members or supportive social systems correlates with increased life expectancy.^16,17 Moreover, prioritizing a plant-rich diet and ample water intake highlighted the significance of diet in the lives of blue zone residents which is in accordance with an Adventist Health study that reported that vegetarian dietary patterns were associated with lower mortality.⁸

It is important to note that the 2 major chronic oral diseases, periodontal disease and dental caries, could benefit from decreasing the intake of processed, high-glycemic carbohydrates. In contrast, consuming complex carbohydrates that are rich in fiber, such as fruits, vegetables, legumes, nuts, and seeds, could help reduce periodontal inflammation.^18,19 This observation supports our hypothesis that residents of Blue Zones, who typically follow a plant-rich diet and snack on nuts, may demonstrate better oral health and an enhanced quality of life. This is also in accordance with another study that showed that salad or fresh vegetable consumption was positively associated with lower cumulative OHIP‐14 scores.²⁰ It is important to note though that based on the regression analysis, the plant-based diet was not a statistically significant predictor for OHRQoL. Based on our findings, we accepted our hypothesis as lifestyle traits such as nut consumption and exercise were significant predictors for oral health related quality of life. Loma Linda blue zone residents’ cumulative mean OHIP-14 of about 7 was lower than a comparable cohort of older adults residing in San Bernardino County, California where the cumulative mean was 16.¹⁴ The study also reported a notable disparity in oral health related quality of life among different racial groups which is in accordance with findings of our study. Another study that used the cross-sectional NHANES 2003-2004 survey of a nationally representative sample of US adults where the mean age was 43a0years reported a cumulative mean of 2.8.²¹ However, it is important to note that the Sanders study used a subset of OHIP-14 consisting of 7 questions and it is not clear how it can be compared to the cumulative score using 14 questions.

Our study findings highlighted a notable difference in adhering to positive lifestyle patterns and OHRQoL between Whites and Asians living in a blue zone. It is noteworthy that the 3 largest ethnic groups in Loma Linda are Whites (35.2%), Asians (25.3%), and White Hispanics (8.75%).⁴ There are several limitations to the study. One significant limitation is the lack of representation of the White Hispanic group. Other limitations include the self-reported nature of data for lifestyle adherence and oral health related quality of life, which can introduce biases and inaccuracies. Additionally, the cross-sectional design of the study limits the ability to establish a causal relationship between lifestyle factors and oral health outcomes. Lastly, the limited sample size could negatively affect the validity and generalizability of our study findings.

A major outcome of our study is augmenting awareness about the unique opportunity oral health care providers can assume in promoting healthy lifestyles. Currently, most dental professionals do not include nutritional counseling or healthy lifestyle promotion such as exercise in their services, highlighting a significant gap in recognizing the dentist’s role in healthy diet and lifestyle choices.²² Our findings indicate that future studies are warranted to investigate the benefits of proactive diet and lifestyle counseling by dental professionals. These initiatives could not only help in preserving oral health but may also improve overall quality of life and longevity.

Within the limitations of the study, we conclude that Loma Linda residents adhere well to the Power 9® lifestyle and demonstrate overall favorable oral health related quality of life. There are significant predictors such as nut consumption and exercise for increased oral health related quality of life.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

So Ran Kwon

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Blue Zone Loma Linda: Assessing the Relationship Between Lifestyle and Oral Health