Cardiovascular Disease Risk predicted by WHO ISH charts
In the present study, prevalence of High CVD Risk predicted by WHO ISH Cholesterol Method was 4% whereas none of the WHO ISH methods that does not use direct cholesterol measurements predicted high CVD risk above 3%. Study by Ranawaka at el. reported the prevalence of high CVD Risk proportion to be 8.2% when using non specified WHO ISH CVD Risk Charts (Ranawaka et al., 2016). In the study by Mettananda et al, prevalence of high CVD Risk was 10.7% and 9.5% when using WHO ISH Cholesterol and WHO ISH Non-Cholesterol methods respectively. The reason for the differences can be the age of the participants ( older participants )in both Mettananda et al and Ranawaka at el studies (Ranawaka et al., 2016; Mettananda et al., 2021). Additionally, present study includes 30–35 years age category which generally has a low CVD Risk due to the age( Dhingra and Vasan, 2012). This might have resulted in low prevalence of high CVD Risk in the present study. This may also explain the low proportion of high CVD Risk when using WHO ISH Charts compared to Mettananda et al. study. A cohort study in Sri Lanka by Thulani et al. has shown high percentages of high CVD Risk predictions compared to the present study by both WHO ISH Cholesterol and Non-Cholesterol Methods Sri Lankans (Thulani et al., 2021). The older age group of 40–64 years in that cohort study might have produced these different findings. In the present study in WHO lSH assume 5 method, only 0.3% were identified as having CVD Risk > 30%. When comparing with the annual health statistics of Sri Lanka, only 0.7% of screened population from Kurunegala district had high CVD risk > 30% when using WHO lSH assume 5 method (Ministry of Health, 2019). This might be an evidence of a specific characteristics of a population of a specific area. All the other studies have been conducted in urban areas with different population characteristics compared to the mostly semi urban Kurunegala district.
Further, results of the present study are similar to a Cuban study (40–80 years) when comparing the WHO ISH Cholesterol and Non-Cholesterol methods and Peruvian study when comparing non specified WHO ISH Method (Nordet et al., 2013; Bazo-Alvarez et al., 2015). What these findings show is that even in different regions of the world, using different risk prediction charts similar results can be seen due to similarities that can occur in CVD Risk factor levels. On the other hand, these results were lower than findings from UK South Asian migrant, Indian and Omani studies (Bansal et al., 2015; Al-Lawati et al., 2013; Findlay et al., 2020). These studies do not mention clearly whether the WHO ISH Cholesterol or Non-Cholesterol methods were used. The different levels of CVD risk factors and different risk charts (By WHO region), diabetic population in Omani study, and sample with MI in Indian study might have resulted in these different findings.
Other important factor we have to consider in the present study is that, WHO ISH Charts are not developed to be used for 30 to 39-year age group, (WHO, 2007). For the 30-to-39-year group we used the chart developed for 40–49 years groups which has been recommended for the 35–39 years age group as per guidelines of the ministry of Health, Sri Lanka. This might have produced low percentages of high CVD Risk category participants. The results from the present study have shown this by the low prevalence of high CVD Risk Prediction among persons in the 30–39 years age category by all four WHO ISH Methods.
Cardiovascular Disease risk predicted by original Framingham Risk Scores
Original Framingham Risk Scores identified 17% as having high CVD risk > = 20%. This is extremely low when compared to Mettananda et al and Ranawaka at el. Studies from Sri Lanka (, Ranawaka et al., 2016; Mettananda et al., 2021). The reason can be attributed to the high HDL Cholesterol level found in this study compared to other two studies. HDL Cholesterol level directly affects the measurement of Framingham Original CVD Risk score. High HDL Cholesterol levels lower the CVD Risk calculated with the Framingham Risk Scores CVD Equation. Further, the age groups used in those studies were older compared to the present study. Approximately one third of the participants in this study were in the 30–39 years age group and none were above or equal to 60 years. This might have resulted in these low percentages of high CVD Risk by original version of the Framingham Risk Scores in the present study. Further, the percentage on antihypertensive in Mettananda et al study was higher than 27.8% that was found in the present study. The Ranawaka at el study reported 2.7% with previous CVD events who were included in the risk calculation. When comparing with studies from other parts of the world, the proportions with high CVD risk categories are low in the present study (Al-Lawati et al., 2013; Selvarajah et al., 2014; Bansal et al., 2015; Garg et al., 2017,). High hypercholesterolemia percentages and low mean HDL Cholesterol in these studies might have resulted in the said differences. High mean HDL Cholesterol level in the present study provides a large negative value on BiXi function. Accordingly, it results in a large reduction in CVD risk.
Cardiovascular Disease Risk predicted by recalibrated Framingham Cardiovascular Disease Scores
In the present study, Framingham recalibrated version predicted a total of 10.9% (9.0% females and 13.4% males) to be in high CVD Risk categories which was lower than the risk calculated by the original version (13.8% in females and 21.8% males). In an Australian Indigenous study, the recalibrated Framingham Risk Scores returned a higher risk of 19.6% and 22.9% compared to 8.9% and 15.4% with the original version for males and females respectively (Hua et al., 2017). In a Hong Kong study, recalibrated Framingham Risk Scores had predicted 36.1% males and 22.2% females to be in the high CVD Risk category which was more or less similar to the risk scores by the original version (Leung et al., 2018). In the Hong Kong study, the population was older (mean 65 years) which may have given rise to the higher high CVD risk proportions. Although the Australian Indigenous study had a similar lower age cut-off the upper end was 74 as against the 60 years of the current study which may be the reason for the higher risk category being larger. In interpreting these results we have to take into consideration that the recalibration was conducted using beta coefficients of the Framingham Original Study replacing only the local risk factor mean values and CVD survival rate data. Comparatively different mean values and survival data might be producing different findings. Especially, when compared to these studies the proportion smoking among females is zero in the present study. The smoking has a higher impact on the equation itself. Therefore, the different results might have been obtained. When calculating the BiMi function the high mean of HDL Cholesterol level in the present study might have also led to low CVD Risk levels in the final calculation in the present study (refer-methodology section).
Agreements between Cardiovascular Disease risk prediction methods
At kappa 0.716 agreement between WHO ISH Cholesterol and WHO ISH assume 5 methods was found which, was roughly similar to the findings of the Mettananda et al study and the cohort study by Thulani et al (Mettananda et al., 2021, Thulani et al., 2021). Furthermore the percentage agreements between the two scores are high (100% of > 20% CVD risk persons of WHO ISH assume-5 method were categorised as > 20% CVD risk by WHO ISH Cholesterol method). The 5mmol/dl is the recommended assumption to be used for the total Cholesterol in a low resource setting. Apart from assuming cholesterol as five, a further calculation assuming a total Cholesterol of 4mmol/dl (WHO ISH assume 4) which, was the mean total Cholesterol level reported in the Sri Lankan WHO STEPS Study was carried out (WHO, 2017). Both the, WHO ISH assume 4 and the WHO Non cholesterol method did not provide good agreement (k = 0.104 and 0.123 respectively) with the WHO ISH Cholesterol method. On the other hand, in the present study, mean total Cholesterol level was 209 mg/dl (~ 5mmol/dl) which may have resulted in good agreement between WHO ISH Cholesterol Method and WHO ISH assume 5. This supports the use of the value recommended by the ministry of health of Sri Lanka of 5mmol/dl with WHO ISH CVD Risk assessment in a low resource setting., This finding further supports the claim that the risk prediction models which require more laboratory data tend to be in good agreement with models which don’t use much lab data (Gaziano et al., 2013; Jones et al., 2015).
The agreements between the original and recalibrated Framingham versions were substantial (k = 0.613). When considering low CVD risk strata, percentage agreements between the scores were higher compared to high CVD risk categories. The reason might be the different mean values of risk factors and survival rates used in the recalibration than Framingham Original population. The agreement between the original Framingham Risk Score and the WHO ISH Cholesterol Method was seen as a kappa of 0.023. When considering the high CVD risk strata, percentage agreement between WHO ISH charts and Framingham Original Scores were extermely low (only 10 out of 187 high CVD risk persons by Orginal Framigham scores being identified as high CVD risk by WHO ISH colesterol method). This does not agree with the study of Mettananda et al. where agreement kappa was 0.306 (Mettananda et al., 2021). The reason might be the 30–39 years old group of participants in the current study producing much lower CVD risk predictions with the WHO ISH charts where 40–49 years’ subscale was used to determine the CVD Risk of this particular age group.
Other important finding is that after recalibration, the Framingham Risk Score method showed improvement in agreement (k = 0.365 and k = 0.233) with both WHO ISH Cholesterol Method and non-Cholesterol Method, WHO ISH assume 5 method. The agreements between the methods were higher in low CVD risk strata.This further highlights the importance of recalibrating Framingham CVD Risk Formulae using local risk factor levels and survival rates. Even though this study cannot provide evidence for validity of WHO ISH Cholesterol Methods, as it is the recommended and in use method in Sri Lanka it can be considered as the gold standard for risk estimation for Sri Lanka. Once recalibrated for local risk factor levels Framingham CVD Equation shows high agreement with the WHO ISH Cholesterol Method. The important fact that has to be taken into consideration while interpreting this finding is that the recalibration was conducted using the mean risk factors data from the local population. The original beta coefficients of the Framingham Study were not changed due to the unavailability of local beta coefficients. Locally applicable beta coefficients have to be developed through a cohort study in the local context. The improvement could be much higher if such developed coefficients were used for the recalibration. If that agreement was made higher, both the recalibrated Framingham version and the WHO ISH Chart may be used interchangeably. Since Framingham Equations take into consideration HDL Cholesterol levels and hypertension status into their risk prediction model when compared to WHO ISH Methods, the former can be considered superior to the latter. On the other hand, since WHO ISH CVD Charts does not depend much on laboratory methods for risk levels to predict CVD risk. It can be advantageous in economic terms in low resource settings. Further, the WHO ISH and a recalibrated Framingham method further improved by using local beta coefficients could be interchangeably used even for high-risk categories.
Age and sex wise distributions of predicted Cardiovascular Disease Risk
In the present study Original Framingham CVD Risk Equations predicted significantly higher proportion of males than females to have high CVD risk (21.3% vs. 13.8%). Similarly in Mettananda et al study and in an Iranian study Framingham Original CVD Risk Score predicted significantly high proportion of males in to high CVD risk category (Nakhaie et al., 2018; Mettananda et al., 2021). High dyslipidaemia levels among males in these studies might have resulted in these high CVD risk calculations (Tennakoon et al., 2010).
In this study, the CVD risk predicted by WHO ISH method has categorized a significantly high percentage of females into high CVD risk category compared to males (5.4% vs. 2.1%). This is similar to a study by Ranawaka et al. (Ranawaka et al., 2016) and a Nepali study which reported, CVD Risk categorization dependent on sex (Khanal et al., 2017). The Ranawaka et al study shows similar high proportion of females having high CVD risk whereas Nepali study shows the opposite. In a Jamaican study using WHO ISH Charts, there was no differences in CVD risk categorization according to sex (Tulloch-Reid et al., 2013). Nepal and Sri Lanka being south Asian countries tend to have similar CVD risk factor level prevalence compared to Jamaica which may have resulted in the findings.
CVD risk categorization was dependent on age in CVD risk predicted by WHO ISH cholesterol method and both Framingham methods in the present study, with prevalence in the high-risk category increasing with age. Similarly in Ranawaka et al study and three Asian country study CVD risk categorization was influenced by age (Otgontuya et al., 2013; Ranawaka et al., 2016). The noteworthy fact is that in 30–39 years age group there were fairly low percentage of high CVD risk persons when using any method in this study.
Associations of risk factors not included in the risk prediction models with the predicted risk
Risk prediction models include selected risk factors out of many cvd risk factors. Here we attempted to explore the associations between the risk predicted by different models with risk factors not included in the respective models.
In the present study, CVD risk predicted by any of the methods was not associated with the family history of CVD. In general, family history is a known and an important factor associated with future CVD (Schunkert et al., 2011). In Epic Norfok study, it was shown that Family history of CHD was associated with high CHD risk by Framingham equation (Sivapalaratnam et al., 2010). However,this study was conducted using the hospital records and only used CHD events in contrast to the present study (Sivapalaratnam et al., 2010). Family history was found to be a significant predictor of CVD risk assessed by the WHO ISH CVD risk charts (Non-Cholesterol Method) in multivariate analysis in Indian Kurnool area study where the association was derived through a proxy indicator e.g.; through direct CVD Risk factors like DM and hypertension to depict the predicted CVD risk. In the present study, family history of CVD events was recorded as reported by the participants which may have been inaccurate in some of the instances which may have given rise to the differences in the findings compared to other studies. Findings similar to our study were reported by a Malaysian study with regard to WHO ISH Cholesterol Method (Norhayati et al., 2013). However, neither WHO ISH Method nor Framingham Method incorporates family history in to their equations (Assmann et al., 2002, Woodward et al., 2007). Findings from the present study suggest that either of these risk predictions does not represent the risk imposed by family history of events.
In the present study, being on antihypertensive treatment was a significant factor associated with the CVD risk predicted by WHO ISH Cholesterol Method. Similarly, in a Punjabi study, it was shown that the high-risk category by WHO ISH Cholesterol was associated with use of antihypertensive. However, in the above-mentioned study, the bivariate or multivariate analysis was not conducted to determine the significance (Vikramaditya et al., 2017). WHO ISH Cholesterol Method does not take in to account the fact of being on antihypertensive for their calculations as the Framingham Equation does. However, from these study findings it can be assumed that the risk predicted by WHO ISH cholesterol method represents the antihypertensive factor in categorizing into high CVD risk category.The alcohol consumption has been proven to be highly associated with the risk of future CVD events (Rehm and Roerecke, 2017). In the present study, alcohol consumption was not a significant predictor in any of the WHO ISH CVD Risk Methods. Alcohol consumption was found to be a significant predictor of WHO ISH CVD Risk (Non-Cholesterol Method) in the multivariate analysis in Indian Kurnool area study and bivariate analysis in Lucknow study (Bandela et al., 2016;Deori et al., 2020). In the Kurnool study method of defining on alcohol consumption was not given and also there had been a high prevelance of alcohol consumption among females in contrast to the present study. In a study from Lucknow India, there was a non-significant association between alcohol consumption with CVD risk predicted by WHO ISH Cholesterol Method. Alcohol consumption was defined as alcohol drinking in the past 30 days in the current study similar to Lucknow study. Multivariate analysis had not been conducted by the Lucknow study investigators. These differences might have given rise to the differences in findings. In the study. In the present study, alcohol consumption was not a significant predictor for CVD risk predicted by any of the Framingham CVD Risk Scores. Similarly, a rural Karnataka study (N = 60), Japanese Minamisomata study (N = 7855) and Baltimore study (N = 1722) found that high Framingham CVD Risk Scores (Original Framingham Equation) were not associated with high alcohol consumption (Allen et al., 2014; Toda et al., 2017 ;George et al., 2017). Only the Japanese study has provided details on alcohol consumption definition which is defined by the frequency of use. However, original or recalibrated Framingham CVD Risk Scores seems to underrepresent risk posed by alcohol consumption status of an individual on CVD risk in the current study sample.
In the present study, only recalibrated Framingham CVD Risk Scores were significantly associated with inadequate vegetable consumption in the Logistic Regression. The Original Framingham CVD scores were associated with inadequate fruit intake significantly. The rural Karnataka study (N = 60) found that the high Framingham CVD Risk Scores (Original Framingham Equation) was not associated with unhealthy dietary intake (adding consumption of junk food) (George et al., 2017). In Kranataka study, no multivariate analysis was conducted. However, in Teheran Lipid and Glucose survey healthy dietary patterns were associated with low risk in multivariate analysis (Ebrahimof et al., 2018). In the Teheran study, Original Framingham CVD Risk Scores were used. This might reflect the risk posed by unhealthy food patterns being represented well by CVD Risk Scores predicted by the Original Framingham Model in Teheran and recalibrated version in the present study.
In the present study, CVD Risk Prediction by only WHO ISH Cholesterol Method was significantly associated with fruit consumption. In a Malaysian study, similar results were obtained for healthy diet in a 24-hour recall (Norhayati et al., 2013). This suggests that the Framingham CVD Risk Scores and WHO ISH Cholesterol Method might represent the risk posed by the inadequate fruit and vegetable consumption. Inadequate fruit and vegetable consumption has been found to be a major risk factor for CVD (Wang et al., 2014). The results have to be interpreted carefully as a 24-hour dietary recall was the only method used to find the adequacy of vegetable and fruit consumption in the present study. In the present study, neither the Framingham Methods nor WHO ISH Methods were associated with physical activity level in the multivariate analysis. However, physical activity level is a known risk factor for CVDs (Wannamethee and Shaper, 2001). Inability of CVD risk prediction methods to represent the physical activity level or sedentary activity duration might imply deficiencies in the risk scores. This may have arisen due to the high physical activity prevalence among the majority which was reflected in the levels of physical activity which are more or less similar in the different risk categories as well. Similarly, A rural Karnataka study (N = 60) found that the high Framingham CVD Risk Scores (original Framingham equation) (> 40%) was not associated with high physical inactivity (using duration of physical activity) (George et al., 2017). Similarly, the Framingham CHD Risk was not significantly associated with physical activity levels in a USA study but was significantly associated with CHD in a study from Finland (LaMonte et al., 2001, Hu et al., 2007). These differences and similarities can arise from the different physical activity levels among different populations. Furthermore, in Finland study physical activity was defined using the frequency of the physical activity conducted. In a rural Panjabi study, high proportion of high CVD Risk predicted by WHO ISH Non-Cholesterol Method was seen among high percentage of physically inactive people where significance of this association was not calculated (Vikramaditya et al., 2017). In a Malaysian study, the physical activity level was not significantly associated with CVD Risk predicted by WHO ISH Cholesterol Method (Norhayati et al., 2013). Similar methodologies followed in these two studies might have resulted in similar findings. The Malaysian study used 7-day physical activity recalls similar to this study. This seems that most of the CVD scores were not sensitive to the risk posed by the lack of physical activity. In the present, waist circumference was found to be significantly associated with the recalibrated Framingham CVD Risk Scores in the multivariate analysis. Similar results were obtained in various studies ( Park and Kim, 2012;Goh et al., 2014). Waist circumference is associated with high CVD Rates (De Koning et al., 2007). This implies the importance of the Framingham Equation after recalibration in representing waist circumference related CVD risk. In the present study CVD risk predicted by WHO ISH CVD Risk Methods were not significantly associated with waist circumference (Table 25, 26). The reason might be the poor performance of WHO ISH Methods in representing waist circumference levels in the current study sample. In a rural Indian study, waist circumference was found to be a significant factor determining CVD risk predicted by WHO ISH CVD Charts in contrast to the present study. Whereas, in the study mentioned above, the direction of the association was not found (no odds ratios were calculated) (Balaji et al., 2018)In the present study, CVD risk predicted by Framingham Original and Recalibrated versions were significantly associated with Triglyceride levels. Similarly, in a Saudi Arabian Military personal study it was found that Triglyceride levels were significantly associated with Framingham CVD Risk Score in the multivariate analysis (Al-Dahi et al., 2013). In a Korean study, bivariate analysis showed that Triglyceride levels were significantly correlated with Framingham CVD Risk Score when using the original Framingham version (Park and Kim, 2012). This shows the representation of risk posed by triglycerides on CVD disease risk through the, the Framingham CVD Risk Score in any population either military or non-military. In the present study, WHO ISH CVD cholesterol method also seems to perform in similar manner. High Triglyceride levels itself is an independent risk factor for CVD risk (Kannel and Vasan, 2009). Therefore, the representation of the risk posed by Triglyceride level might imply high performance of Framingham CVD Risk Methods and WHO ISH cholesterol method regarding indirectly showing CVD risk imposed by high Triglycerides.For further study to compare the performances of each CVD risk score a cohort study is essential.