3.2 Definition of risk factors for at-risk populations

tends to underestimate cohort life expectancy, its two practical advantages make it the predominant choice among demographers in describing life expectancy (Guillot 2011). In Saudi Arabia, the average period life expectancy at birth (ex0) is 76.51 years for women and 73.71 years for men. By 2050, this is projected to increase to 80.93 years for women and 78.22 years for men. This projection assumes no change in the NCD profile. Rather, these estimates come directly from uN population forecasts (uN DeSA 2019).

Current estimates of NCD burden associated with the three risk factors are applied to the life tables to arrive at the forecasts of NCD-attributable premature mortality and disability in 2030, 2040, and 2050. This initial forecast assumes no change in risk factors in that no interventions have occurred (that is, there have been no government interventions and no increase in prevalence). Age-specific risks of disease are applied for the key NCD conditions as a function of exposure to smoking, high BMI, and salt intake. These age-specific risks are derived from the best estimates from the peer-reviewed epidemiologic literature (IHMe 2018a) and then used to determine DALYs, HALe, and ex0 by gender. This initial forecast assumes decreasing fertility trends, an aging population, and decreasing mortality and morbidity from disease for all age groups.

Next, NCD disability is forecasted to 2050 using different assumptions about modification in risk factors. In order to model a realistic scenario with mildly to moderately successful policy interventions, two scenarios are considered: a moderate intervention (Model 2) and an aggressive intervention (Model 3). Policy interventions would be targeted toward the most at-risk populations (box 3.2). The effects of various policy interventions are estimated by carefully reviewing previous policy initiatives reported in the peer-reviewed literature. Some of these interventions include comprehensive policies regarding environmental tobacco smoke in Turkey (Kostova et al. 2014) as well as salt in packaged products in the united Kingdom (Brinsden et al. 2013). Details are provided in annex 3A.

Model 2 (moderate intervention) assumes that Saudi Arabia will adopt some policy changes and that these changes will be mildly successful. Moderate success is classified as a 14.6 percent reduction in smoking, a 10.0 percent reduction

BOX 3.2

Definition of risk factors for at-risk populations

Persons with the following risk factors are the target population:

• Hypertension, defined as systolic blood pressure above 140 millimeters of mercury (mmHg). Systolic blood pressure was chosen as the key risk factor for hypertension because it has been shown to be a better indicator of cardiovascular events than other measures (Gu et al. 2008). • Overweight, defined as body mass index (BMI) of 25.0–29.9 kilograms per square meter. • Obesity, defined as BMI equal to or greater than 30.0 kilograms per square meter. • Current daily smoking, defined as smoking an average of 15.1 cigarettes per day (Moradi-Lakeh et al. 2015).

in overweight and obesity, and a 9.2 percent reduction in hypertension every 10 years. For example, in Saudi Arabia in 2020, an estimated 17.1 percent of men smoked (MOH 2020). Assuming a 14.4 percent reduction in smoking prevalence every 10 years, a moderate intervention scenario forecasts the smoking prevalence among men as follows:

• 2030: 17.1 percent × 0.856 = 14.6 percent • 2040: 17.1 percent × (0.856 × 0.856) = 12.5 percent • 2050: 17.1 percent × (0.856 × 0.856 × 0.856) = 10.7 percent.

Model 3, the aggressive scenario, assumes that policy interventions will address all key risk factors, placing greater focus (that is, more aggressive policy interventions) on risk factors that contribute the most to the DALY burden among the priority NCDs. In Saudi Arabia, the priority risk factor is high BMI. using Global Health Survey estimates, more than 60 percent of the population over 45 years of age is overweight (MOH 2020). In addition, high BMI contributes substantially to the burden of heart disease, stroke, and diabetes. The high prevalence of overweight and obesity makes reducing population-level BMI a top priority for intervention scenarios in Saudi Arabia.

The aggressive scenario of Model 3 assumes a 20 percent reduction in the overweight and obese population every 10 years. Because of the widespread prevalence of overweight and obesity among the population in Saudi Arabia and the high relative risks for NCDs, reducing BMI is expected to have the largest impact on DALYs. In addition, Model 3 assumes a 14.6 percent reduction in smoking and 9.3 percent reduction in hypertension in the population every 10 years.

For key conditions (by age and gender), the population-attributable risk fraction (PAF) is calculated for all risk factors to project years of life lost (YLL) and years lost due to disability (YLD) to 2050. The population-attributable risk summarizes the fraction of YLL and YLD due to the prevalence of the risk factor. Relative risks and adjustments for overlapping risk factors are from the 2017 Global Burden of Disease estimates (IHMe 2018a). Age-specific relative risks (five-year groupings) are from the Global Burden of Disease estimates for the relative risks for conditions. Increased exposure to the risk factors (that is, having high blood pressure, smoking, and being overweight or obese) results in additive risk for each increase in level of exposure. Levels of exposure are measured in increments of 5 kilograms per square meter for overweight and obesity, 10 mmHg (millimeters of mercury) for systolic blood pressure, and number of cigarettes, packs, and pack-years for smoking.

Changes in the PAF (observed via changes in age- and gender-specific risk factors) are used to calculate changes in mortality (for the life table) and YLD. Box 3.3 provides an example of a PAF calculation (for 2020 and 2030). PAFs are calculated for all risk factors by condition. For conditions for which overweight or obesity and high blood pressure are both risk factors, both PAFs are adjusted by a factor of 0.35 for overweight or obesity and 0.65 for high blood pressure.

The Kingdom of Saudi Arabia World Health Survey (KSA WHS) estimates are used to calculate the baseline prevalence of smoking, overweight and obesity, and hypertension (MOH 2020; see annex 3A). To estimate the gains in HALe, the calculations of YLD averted in box 3.3 are used to derive the gender- and age-specific YLD avoided and the concordant reduction in mortality. The proportion of mortality attributable to the key NCDs is then calculated. For each