Effect of vitamin D supplementation versus placebo on patients with hypertension

Chapter 3: Research Methodology

3.1. Research Design

In line with the research philosophy of positivism, which emphasises the need for value-free research and implementation of the scientific method even in social studies (Saunders et al., 2018), this thesis adopted the deductive approach and the quantitative research design to study the effects of vitamin D supplementation on blood pressure (BP) of individuals with hypertension.

Hypertension is one of the most serious medical conditions for both young and old people. Several studies in the past attempted to explore the role of vitamin D supplements in lowering blood pressure (BP) in individuals with hypertension (Condoleo et al., 2021; Gariballa et al., 2022; Theiler-Schwetz et al., 2022). As these studies produced mixed results, there is a need to conduct an in-depth investigation using a larger sample to understand the role of vitamin D supplements in lowering blood pressure.

For this purpose, this study aims to conduct experimental research on individuals with hypertension. The experimental design was selected to establish causality between the independent variable, namely: vitamin D supplementation, and the dependent variable, BP, among individuals with hypertension.

3.2. Research Setting

A double-blind, placebo-controlled and randomised pilot study was conducted on the patients of St. James Hospital, Dublin, Ireland. The effect of vitamin D supplementation was significantly visible on systolic BP (130.9 mmHg) in the first and second months after intervention. However, its effect on diastolic BP was only marginally visible (80.4 mmHg), which agrees with Sheikh et al. (2020). Based on these results, a full-scale study was designed to observe the patients for a period of two months between August 2021 and October 2021.

3.3. Sample Selection

For the purpose of the study, a sample of 216 patients was selected. The population for this study included adults aged 30 to 65 diagnosed with hypertension, residing in the urban area of Dublin. All the people included in the study were registered in the hypertension registry of the James Hospital, Dublin, Ireland. These participants experienced a systolic BP equal to or greater than 140 mmHg or a diastolic BP equal to or greater than 90 mmHg. To ensure the participants match the study criteria, they were also categorised into vitamin D deficiency and vitamin D non-deficiency. Out of 216 participants, 34 participants were observed to have normal levels of vitamin D (75–150 nmol/L) (Bleizgys, 2021) while others had vitamin D levels lower than 75nmol/L.

To maintain the academic integrity of the research, written informed consent was received from all the participants. The consent form included the study’s purpose, procedures, potential risks, and benefits. The study was approved by the Ethics Committee at the University Hospital, Dublin. To ensure privacy, the participants’ data was kept confidential and personal identifiers were removed from the dataset.

In order to simplify the experimental study, these participants were excluded from the study and only 182 participants were selected. Additionally, pregnant and lactating women, participants with secondary hypertension, chronic kidney diseases, diabetes and renal failure and people with a history of using vitamin D supplementation during the last six months were excluded from the study. To confirm the eligibility of participants, all participants had to undergo a pre-study screening. The screening included a detailed physical examination, a study of the medical history and the measurement of the baseline BP of all participants. In addition to this, blood samples of all participants were collected to measure baseline vitamin D levels.

Participants who met the eligibility criteria were randomly assigned to either the treatment group (vitamin D supplement) or the control group (placebo) using a computer-generated randomisation sequence. Blinding and randomisation techniques help avoid research bias as both participants and assessing physicians are unaware of the treatments the participant is going to receive (Sil et al., 2019). Factors such as gender, age and severity of hypertension were considered to evenly distribute the participants across the treatment and control groups.

As the study followed a double-blinded method, both participants and researchers were unaware of the group assignments. To ensure confidentiality, the vitamin D supplements and placebos were prepared and labelled by the hospital pharmacy. The shape and colour of both vitamin D supplements and placebos were kept similar to ensure that neither the participants nor the investigators knew which treatment each participant was receiving. The treatment group received a daily dose of 2000 IU of vitamin D3 supplements. On the other hand, the control group was given identical-looking placebo pearls. The duration of the intervention was chosen to be two months as Dědečková et al. (2023) noted that taking 2000 IU daily can lead to a sharp increase in vitamin D serum levels in individuals. Participants were instructed to take one pearl each day at the same time while maintaining their usual diet and physical activity levels.

The main interest of the study was to evaluate the effect of vitamin D supplements on the systolic and diastolic BP of the participants. Thus, all participants were asked to visit the clinic at the beginning of the intervention and at the end of the first and second months to monitor their BP. The systolic and diastolic BP of participants was measured in the sitting position after 10 minutes of rest using a standardised protocol with an automated digital BP monitor (A&D Company Limited Kitamoto-shi, UA-767 PBT). At each visit, three readings were taken and the mean of the last two sitting measurements was used for statistical analyses.

3.4. Methods of Data Analysis

The research uses descriptive statistics and frequencies table to present the baseline characteristics such as age, gender, body mass index, fasting blood sugar and serum cholesterol levels of each participant. Descriptive statistics include the mean, the standard deviation (SDs), the interquartile range (IQRs) and the indicators of skewness and kurtosis. The differences in blood pressure between the respondents in control and treatment groups were measured using the independent samples t-test. The effects of the vitamin D supplements on the level of blood pressure, controlling for the characteristics described above, were assessed using multiple linear regression analysis. The baseline regression model has the following specification:

Equation in sample PhD methodology chapter

Where BP is the level of blood pressure; VitD is the amount of vitamin D supplements; CV is a vector of control variables that include body mass, gender, age, etc; Treat is a dummy variable that takes the value of 1 if the respondent is in the treatment group and 0 if the respondent is in the control group; an interaction term (VitD*Treat) is added to explore the differences in the effects of the Vitamin D supplement on blood pressure in the treatment group compared to the control group. The analysis is conducted in SPSS 24, and the statistical significance of the effects is assessed at the conventional 10%, 5% and 1% levels.

References

Bleizgys, A. (2021) Vitamin D dosing: Basic principles and a brief algorithm (2021 update), Nutrients13(12), p.4415.

Condoleo, V., Pelaia, C., Armentaro, G., Severini, G., Clausi, E., Cassano, V., Miceli, S., Fiorentino, T.V., Succurro, E., Arturi, F. and Andreozzi, F. (2021) Role of vitamin D in cardiovascular diseasesm, Endocrines2(4), pp.417-426.

Dědečková, E., Viták, R., Jirásko, M., Králová, M., Topolčan, O., Pecen, L., Fürst, T., Brož, P. and Kučera, R. (2023) Vitamin D3 Supplementation: Comparison of 1000 IU and 2000 IU Dose in Healthy Individuals, Life13(3), p.808.

Gariballa, S., Yasin, J. and Alessa, A. (2022) A randomized, double-blind, placebo-controlled trial of vitamin D supplementation with or without calcium in community-dwelling vitamin D deficient subjects, BMC musculoskeletal disorders23(1), p.415.

Saunders, M., Lewis, P. and Thornhill, A. (2018) Research Methods for Business Students, Harlow: FT Prentice Hall.

Sheikh, V., Mozaianimonfared, A., Gharakhani, M. and Poorolajal, J. (2020) Effect of vitamin D supplementation versus placebo on essential hypertension in patients with vitamin D deficiency: a double‐blind randomized clinical trial, The Journal of Clinical Hypertension22(10), pp.1867-1873.

Sil, A., Kumar, P., Kumar, R. and Das, N.K. (2019) Selection of control, randomization, blinding, and allocation concealment, Indian Dermatology Online Journal10(5), pp.601-605.

Theiler-Schwetz, V., Trummer, C., Grübler, M.R., Keppel, M.H., Zittermann, A., Tomaschitz, A., Karras, S.N., März, W., Pilz, S. and Gängler, S. (2022) Effects of vitamin D supplementation on 24-hour blood pressure in patients with low 25-hydroxyvitamin D levels: A randomized controlled trial, Nutrients14(7), p.1360.

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  • James_L_PhD_Writer

    James is a psychologist who has worked as a PhD lecturer and is now a full-time writer. He's authored scientific publications, government reports, and thousands of academic articles, and he can assist you with a variety of topics.

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