INTRODUCTION
Myocardial infarction (MI) is one of the major manifestations of coronary artery disease (CAD). CAD is considered to be one of the main causes of morbidity around the world (Gouvinhas et al., 2013). According to the World Health Organization (WHO, 2017), every year approximately 17.9 million people die of cardiovascular diseases worldwide that is 31% of all deaths and most of these occur in developing countries. CAD is a multifactorial disorder that is a consequence of an interaction between genetic background and environmental factors such as diet, smoking and physical activity (Smith et al., 1997; Prins et al., 2012). Atherosclerotic plaque formation, hypercholesterolemia, hypertension, and diabetes are considered as major risk factors for CAD (Smith et al., 1997). Vitamins and minerals act as prosthetic groups and cofactors of almost all enzymes and deficiency of vitamin and mineral has been proved to be a major risk factor for coronary artery diseases (Aggarwal et al., 2016; Chowdhury et al. 2015; Reid et al. 2017).
Vitamin D, a fat-soluble vitamin also known as an antiricketic factor or sunshine vitamin, is unique in the sense that the body synthesizes it, and it also functions as a hormone. Besides its pivotal role in calcium homeostasis and bone mineral metabolism, the vitamin D endocrine system is now recognized to be involved in a wide range of fundamental biological functions in cell differentiation, inhibition of cell growth, and immunomodulation. Several human and animal studies have suggested that vitamin D deficiency may be a contributory factor in the pathogenesis of CAD. Vitamin D deficiency has been shown to result in cardiac hypertrophy and fibrosis by elevation of matrix metalloproteinase enzyme (Weishaar et al., 1990; Loftus and Thompson, 2016). It also predisposes to hypertension by upregulation of the renin-angiotensin system (Kong et al., 2010). Similarly, it is also involved in promoting the formation of atheromatous plaque by increasing the uptake of lipids by macrophages and their conversion into foam cells (Wang et al., 2008). CAD is an emerging problem in developing countries like India and responsible for significant morbidity and mortality, and the situation is expected to be worse in the future (Aggarwal et al., 2016). Multiple studies have shown that vitamin D deficiency is widely prevalent in the Indian subcontinent (Ritu and Gupta, 2014; Kumar et al., 2008), and also, there are studies reporting an early onset and aggressive CAD in South Asian population (Sharma and Ganguly, 2005; Joshi et al., 2007). However, only a few studies explore the role of vitamin D deficiency in CAD patients from the Indian subcontinent and have shown conflicting results (Dhibar et al., 2016; Karur et al., 2014; Syal et al., 2012).
Calcium plays a number of critically important roles in physiology and pathology, in addition to its most widely recognised function as a critical structural component of bone (Reid et al. 2017). Many cells have calcium-sensing receptors, with evidence that the concentrations of calcium ions in the extracellular fluid directly regulate cell function (e.g., parathyroid, renal tubule, and many more) (Chowdhury et al. 2015). Extracellular calcium concentration directly impacts on cell membrane potentials, and so impacts on function of all excitable tissues, particularly the nervous system and the heart (Campbell, 1983). Calcium is a key messenger in the contraction of muscle, including the myocardium. A recent study documented that individuals who consume hard water rich in calcium and magnesium have a lower mortality rate from circulatory disease than those who consume soft water (Jin et al. 2013). Several other studies have shown that serum calcium may influence the level of high-density lipoprotein (HDL) cholesterol and decrease the level of low-density lipoprotein (LDL) cholesterol (De Bacquer et al., 1994; Reid et al., 2002). However, some researchers have drawn the opposite conclusion reporting no association between changes in the hardness or calcium content of drinking water and cardiovascular mortality (Lake t al., 2010). The aim of the present study was to investigate the association of vitamin D and calcium (Ca) with the occurrence of myocardial infarction in Bangladeshi population.
METHODS AND MATERIALS
The study was a case-control study conducted in 250 subjects (Table 1). The case group comprises 100 cardiac patients who have experienced MI one or more times. The cardiac patients were recruited for this study immediately after being hospitalized with MI symptoms at Coronary Care Unit (CCU) of Sir Salimullah Medical College Hospital without any medical history of other chronic diseases. A total of 150 healthy controls with no history of cardiac or chronic diseases were recruited from different hospitals of Dhaka city where they came for regular health check-up (Table 1). All participants were given an explanation of the nature of the study, and informed consent was obtained. They completed a structured questionnaire covering information on age, gender, medical, family history of chronic diseases and smoking status. Smoking status was summarized as smoker or nonsmoker (Table 1). The study was conducted in accordance with the declaration of Helsinki and its subsequent revisions (World Medical Association, 2013).
Sample Collection
Approximately 3.0 mL of venous blood was drawn from each individual following all aseptic precautions with the help of a trained person, using a disposable syringe. The drawn blood was transferred into a plain tube for the separation of serum and transported to the laboratory using ice-box. The serum was isolated by centrifugation and the biochemical parameters including serum troponin I and Ca levels were measured by Dimension Xpand auto biochemistry analyzer.
Assay of Vitamin D
HPLC method was used to measure serum vitamin D. Sample for vitamin D was prepared according to Turpeinen et al. (2003). Isocratic elution was used to detect vitamin D. In our study, we used a C18 HPLC column (4.6 ×100 mm, 3 μm particle size) and run time was 10 min for each sample. Injection volume was 20 μl. Vitamin D was detected using a UV detector at 265 nm.
Statistical Analysis
All the results were expressed as mean±SEM. GraphPad Prism software were used to perform statistical analyses. The comparisons between two groups were tested by independent samples t-test. A 95% confidence interval was used. P values less than 0.05 were considered as statistically significant. The correlation between two continuous outcomes among MI patients was evaluated using Pearson correlation coefficient.
RESULTS
In this study we have studied the association of vitamin D and Calcium with myocardial infarction in Bangladeshi population. We have also measured the serum levels total protein and hepatic enzymes in study subjects. Statistically significant differences among patients and controls are indicated in Table 1 & 2 and in Fig. 1 along with their significant values.
As shown in Table 1 the Alkaline phosphatase (p<0.001) and Aspartate aminotransferase (p<0.001) levels were significantly higher in MI patients than the control subjects (Table 1). On the other hand, the levels of total protein and Alanine aminotransferase (ALT) were almost similar among the both study groups (Table 1).
Table 1 Baseline characteristics and clinical parameters
|
Study parameters |
Healthy Control (n=150) |
CAD Patients (n=100) |
P value |
|
Age |
53 ± 17 |
55 ± 12 |
ns |
|
Gender (n, %) |
|
|
|
|
Male |
113 (75) |
76 (76) |
ns |
|
Female |
37 (25) |
24 (24) |
|
|
Smoking Status |
|
|
|
|
Non-Smoker |
60 (40) |
41 (41) |
ns |
|
Smoker |
90 (60) |
59 (59) |
|
|
Family history |
|
|
|
|
Chemical parameters |
|
|
|
|
TP (g/dL) |
6.95 ± 0.2 |
6.89 ± 0.15 |
ns |
|
ALT (IU/L) |
34.4 ± 3.2 |
27.6 ± 2.2 |
ns |
|
AST (IU/L) |
29.1 ± 2.2 |
55.2 ± 4.8 |
<0.001 |
|
ALP (IU/L) |
74.5 ± 3.8 |
92.3 ± 3.1 |
<0.001 |
Results are expressed as Mean ± SEM and as number (percentage). Student t-tests were performed to estimate the level of significances. p<0.05 was taken as level of significance. ns; Non-significant. TP; Total Protein, ALT; Alanine aminotransferase, AST; Aspartate aminotransferase, ALP; Alkaline phosphatase.
According to Table 2 the Troponin I level was significantly (p<0.001) higher among MI patients while the Troponin I level was nil in healthy volunteers. On the other hand, The Vitamin D and Calcium levels were significantly lower (p<0.001, respectively) in MI patients than in control subjects.
Table 2 Level of Troponin I, Vitamin D and Calcium in study subjects.
|
Parameters |
Healthy Controls (n=150) |
MI Patients (n=100) |
p value |
|
Troponin I (ng/mL) |
0.028 ± 0.002 |
22.3± 4.3 |
<0.001 |
|
Vitamin D (ng/mL) |
43.41 ± 2.52 |
20.17 ± 3.18 |
<0.001 |
|
Calcium (mg/dL) |
8.9 ± 0.25 |
7.6 ± 0.16 |
<0.001 |
Results are expressed as Mean±SEM. T-test was performed to analyse significance between two groups. p<0.05 was taken as level of significance.
Correlations of Troponin I with Vitamin D as well as Ca, and between Vitamin D & Ca among the patients were estimated and showed in Fig. 1 along with their significant values. There were significantly negative correlations between Troponin I and Vitamin D as well as Ca (r=-0.68, p<0.001 and r=-0.27, p<0.05, respectively) levels were found (Fig. 1a and 1b, respectively) while between Vitamin D and Ca correlated (r=0.43, p<0.01) positively (Fig. 1c).
Figure 1: Correlation of Troponin I with (a) Vitamin D as well as (b) Ca, and (c) between Vitamin D & Ca among the patients.
DISCUSSION
Vitamin D deficiency appears to be common in acute myocardial infarction (AMI), and preliminary studies indicate a possible association of vitamin deficiency with AMI prognosis in the short and long term (Milazzo et al., 2017). Moreover, vitamin D deficiency seems to predispose to recurrent adverse cardiac events, due to its association with the number of affected coronary arteries, AMI complications, and cardiac remodelling (De Metrio et al., 2015).
Our case control study on AMI suggests that deficiency of vitamin D is highly prevalent in Bangladesh. It revealed that vitamin D level is significantly lower in cases as compared to controls. The Health Professionals Follow-up Study followed up 18,225 men during 10 years and observed an association between low vitamin D levels and increased AMI risk, even after adjustment for other risk factors (Giovannucci et al., 2008).45 Prospective studies have also found a high prevalence of vitamin D deficiency in patients hospitalized with AMI (Roy et al., 2015; Lee et al., 2011). A previous case-control study in patients of acute MI performed in the USA reported similar inverse association between 25(OH) vitamin D levels and risk of acute MI (Scragg et al., 1990). A more recent study from Pakistan revealed that individuals with normal levels of had lower risk of MI as compared to those with vitamin D deficiency (Iqbal et al., 2013). Similarly a study by Syal et al. (2012) from North India in 100 patients undergoing coronary angiography revealed more severe coronary artery disease and greater endothelial dysfunction among individuals with low vitamin D.
Our results show that serum calcium was lower in cases than in controls. A recent study demonstrated a weak causal relationship between the hardness of drinking water and mortality from cardiovascular disease in males (Schroeder, 1960). Another study documented that individuals who consume hard water rich in calcium and magnesium have a lower mortality rate from circulatory disease than those who consume soft water (Jin et al. 2013). However, some researchers have drawn the opposite conclusion. Sabanayagam and Shankar (2011) reported that higher serum calcium levels were positively correlated with hypertension in a representative sample of US adults, which is consistent with our findings. Similarly, in a previous study Lind et al. (1997) found that subjects with a history of MI have significantly higher serum calcium than those without infarction.
In this study, we have found increased levels of Troponin I, AST and ALP as well as decreased level of Albumin among the patients while we could not found any association between ALT and MI. A population based cohort study in the United State also reported no association between MI and ALT, while several investigations showed that ALT and AST are associated with myocardial infarction (Ruhl et al., 2009; Moon et al., 2014; Gao et al., 2017). A recent meta-analysis study conducted on over 9.24 million participants and reported contradictory results (Kunutsor et al., 2014).
In conclusion, our recent study suggested that Vitamin D and Ca deficiency may have a significant association with the occurrence of myocardial infarction and patients should receive hepatic care in Bangladeshi population. Therefore, measurement of Vitamin D, Ca, AST, ALT and ALP would be a biomarker of early diagnosis of CAD and also be helpful to intervene a novel treatment of CAD. However, our study has a small sample size resulting in low power to detect minor to modest associations, therefore further study with large sample size is required.
ACKNOWLEDGEMENT
We would like to acknowledge the support and cooperation of the participants of this study. This research did not receive any specific grant from funding agencies in the public, commercial or not-for profit sectors.
CONFICT OF INTEREST
The authors reported that there is no conflict of interest.
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