Cardioprotective and Mental Health Benefits of the MIND Diet Combined With Forest Bathing

Background and Significance of the project:

Cardiovascular diseases (CVDs) are the result of atherosclerosis, which is characterized by lipid accumulation and chronic inflammation of the arteries. Elevated low-density lipoprotein cholesterol (LDL-C) is associated with an increased risk of CVDs in all age groups, but particularly in those aged >70 years. The prevalence and burden of CVDs continue to increase globally. In 2019, 523 million people worldwide had a CVD, and CVDs caused 18.6 million deaths and at least 325 million cases of disability. To reduce the risk of developing a CVD, the American College of Cardiology and the American Heart Association have recommended that adults aged 40 to 75 should be prescribed statin therapy if their LDL-C level is >3.4 mmol/L. However, many people are reluctant to initiate statin therapy because they are afraid of potential adverse effects; this reluctance to take statins increases their risk of CVDs and the related morbidity and mortality. Persistent psychosocial stress is a causal risk factor for CVD development. Persistent stress is associated with elevated LDL-C. Recent evidence indicates that adopting a cardioprotective diet in addition to stress management can lower the risk of CVDs .

Stress is widespread in Hong Kong. Owing to their busy lives, many Hong Kong residents consume fast foods, for example, preserved vegetables, processed meat, canned meat, potato crisps and prawn crackers. This unhealthy diet coupled with persistent stress puts people at risk of developing high cholesterol levels and increased blood pressure. The Mediterranean Dietary Approaches to Stop Hypertension (DASH) Intervention for Neurodegenerative Delay (MIND) diet is high in fibre and low in added sugar and is culturally and contextually feasible to adhere to in the metropolis of Hong Kong. The MIND diet encourages increased consumption of plant-based foods, fish, poultry, nuts and berries, which can be easily found in local markets and are accessible and affordable. Adopting the MIND diet has been reported to potentially reduce one's cholesterol level and body weight. Forest bathing (FB) is a relaxation practice in which a person immerses him- or herself in a forest environment to promote physical and mental health. The country parks of Hong Kong are heavily wooded, contain a variety of trees and birds, and are suitable for the practice of FB. FB has been reported to lower blood pressure, anxiety and promoting positive mood but the effect of FB on cardiovascular health benefits is seldom examined in adults. Thus, it is hypothesized that FB could enhance MIND diet on promoting cardiac and mental health. The cardioprotective health benefits of the MIND diet in combination with FB may have an additive effect in reducing CVD risk factors (e.g., LDL-C, blood pressure, stress, BMI, etc.). The investigators conducted a pilot study to examine the combined effect of the MIND diet plus FB in hypertensive adults. The study found that MIND-FB and the MIND diet alone were associated with short-term decreases in LDL-C, blood pressure and anxiety, and they alleviated negative emotions including fatigue, tension-anxiety, confusion and anger among hypertensive adults. The pilot study was conducted among people with hypertension. In the proposed study, the investigators will examine whether the MIND diet combined with FB can also benefit those with high LDL-C. The findings may provide additional preliminary evidence that FB and the MIND diet are therapeutically effective in reducing the CVD risk factors of obesity, high cholesterol and blood pressure, stress and negative emotional states.

This proposed study will target people aged 50-75 years who are at increased risk of CVDs. the investigators will investigate the ability of the MIND diet plus FB to reduce CVD risk factors (obesity, high cholesterol, high blood pressure, high triglycerides and glucose concentrations, stress, and a negative emotional state). The investigators hypothesize that the MIND diet combined with FB will have an increased cardiac and mental health benefit in Chinese adults with elevated LDL-C compared with the MIND diet alone and routine care.

Research plan and methods

Setting and participants: the investigators propose a three-arm randomized controlled trial with a block design (1:1:1) based on the protocols established in our pilot study. Eligible participants will be randomly assigned into three intervention groups: (1) MIND-FB, (2) MIND diet alone and (3) routine care (control). The MIND-FB and MIND groups will receive the intervention, and the control group will receive routine care. Eligible participants will be randomly assigned to one of the three groups by a research assistant based on a predetermined random allocation list generated by a computer program. A serial number will be randomised following block randomisation procedures with a block size of 6 or 12. The participants will be provided with serial numbers, and the research assistant will keep the code for random allocation. The researchers and the data analyst will be blinded to the treatment assignment. The participants will be recruited from the local community through various community centres. An invitation poster will be designed and posted on the website or WhatsApp group of the centres 2 months before the intervention. Potential participants will be required to complete an online demographic questionnaire and undergo health screening to determine eligibility.

Sample size: The pilot study conducted by the project team found that participants in the MIND-FB and MIND groups had a greater benefit in terms of reduced LDL-C than participants who received usual care. For the proposed study, the effect size is estimated to be approximately 0.2. To test a 5% level of significance of the effect among the three groups (MIND-FB, MIND and routine care) on the primary outcome (i.e., reduction in LDL-C at 12 weeks) with a power of 80% and attrition rate of 10% (based on our pilot study), a total of 273 participants will be required. The required sample size will be 91 participants per group (at a ratio of 1:1:1). An F test in G*Power 3.1.9.4 was used to estimate the sample size.

Demographic and other covariates: At the baseline assessment, the investigators will collect sociodemographic data (sex, age, marital status, educational attainment), diet score, physical activity, alcohol consumption, body mass index, waist circumference (cm), self-reported medical diagnoses, measured BP, current medications and number of chronic diseases.

Follow-up during the intervention: A logbook will be given to each participant in the MIND-FB and MIND groups to record their compliance with the MIND diet for adherence checks. A trained research assistant will call the participants every week via WhatsApp to discuss their progress and learning and provide them with feedback if the participant has barriers or challenges in adhering to the MIND diet.

Diet score: Adherence to the MIND dietary pattern will be assessed by calculating the MIND diet score. The MIND diet score assesses 10 healthy food groups and five unhealthy food groups, and a value of 0.0, 0.5 or 1.0 is assigned to each group. In this scoring system, a person receives a score of 1 if they consume items in the healthy food group, while the score is reversed (i.e., -1) for unhealthy food groups. The total MIND diet score is then calculated by summing all food group scores, with a maximum score of 15 representing the strongest adherence to the MIND diet.

Statistical methods: All statistical analyses will be performed using SPSS version 26 (SPSS Inc., Chicago). The alpha level will be set at 0.05 for the two-tailed tests. Intention-to-treat analysis will be applied for any missing data from the follow-ups; multiple imputation will be applied to handle any missing data at baseline. The chi-square test and ANOVA will be used to assess the baseline demographic, socioeconomic and lifestyle characteristics, medical history and medication use among the three groups at baseline. Generalized estimating equation (GEE) models will be used to examine changes in the LDL-C and other secondary outcomes at 4 and 12 weeks and will be adjusted by the random effect of each community centre. Secondary analysis will be conducted to adjust the GEE models for other potential confounders, e.g., demographic characteristics and socioeconomic status. Separate GEE models will be applied to examine dietary changes among the three groups at 4 and 12 weeks.

Ethical considerations: The proposed study will be a health promotion project designed to evaluate the effectiveness of a health promotion activity on cardiac and mental health. Eligible participants will be given an information sheet about the study. Written informed consent will be obtained when the participants are screened for eligibility. The participants will be fully informed about the aims and procedures of the activities and the benefits and risks of participating. The participants will be able to withdraw from the study at any time without consequence. None of the collected data will be revealed to any third party; the data will be kept confidential and anonymous. All data files will be encrypted, and hard copies of the data will be stored in a locked cabinet inside a locked room. The risk of harm to the participants is low. The FB guide and assistant will be first aid providers and will ensure a high level of safety during the FB walk. Individuals with SBP >159 mmHg will be considered ineligible for the study and will be advised to consult a doctor. The contact details of the principal applicant and relevant staff will be provided to the participants in case they have further questions or complaints.