We conducted a comprehensive systematic review and pooled 3,505 data points on over 500,000 adults, aged 25 to over 85 years, recruited in national and provincial population-based surveys in Iran as well as published studies from 1990 to 2016. The number of data sources for each province and year is demonstrated in the heat map in appendix (Supplementary Figure 1).
Nationally, the number of adults with total cholesterol over 200 mg/dL decreased from 10·5 (9·8 – 11·5) million in 1990 to 9·9 (9·0 – 10·6) million in 2016. In the meantime, the number of adults with elevated TC, or TC over 170 mg/dL, increased from 15·6 (15·0 - 16·1) million (7·6 million in women) in 1990 to 22·9 (21·6 - 24·2) million (12·0 million in women) in 2016.
Age standardized prevalence of raised total cholesterol at national level has decreased from 57·2% (95% CI: 53·3 – 61·1) to 22·4% (20·5 – 24·3) in women and from 53·2% (49·1 – 57·3) to 18·0% (16·4 – 19·6) in men between 1990 and 2016 (Figures 1). Age standardized prevalence of elevated TC at national level has decreased from 82·4% (79·8 – 84·8) to 49·5% (46·8 – 24·4) in women and from 79·7% (76·7 – 82·3) to 43·7% (41·0 – 46·5) in men between 1990 and 2016 (Figure 1 and supplementary Figure 2).
From 1990 to 2016, age standardized mean TC in women has decreased from 202·5 mg/dL (191·2 – 214·6) to 174·5 mg/dL (166·6 – 182·8). In men mean TC decreased from 197·3 mg/dL (186·1 – 209·4) to 168·5 (160·7 – 176·7) (Figure 1).
The percent change in age-standardized prevalence of elevated TC from 1990 to 2016 was -40% (-45 to -35) in women and -45% (-50 to -39) in men (Supplementary Table 1). The percent change in age-standardized prevalence of raised TC from 1990 to 2016 by -61% (-66% to -54%) in women and -66% (-71 to -60) in men (Supplementary Figure 3). The prevalence of elevated TC has decreased in all provinces and decreased by more than half in a few provinces in both sexes from 1990 to 2016. Similarly, the prevalence of raised TC has decreased by more than half in almost all provinces in both sexes from 1990 to 2016, except for one province in men and four provinces in women (Figure 2 and 3).
Mean TC, and prevalence of both elevated and raised TC increased in adults from 25 to 55 years of age and then showed a steady trend till the oldest age group of 85 and over in all years from 1990 to 2016 (supplementary figure 4). The age pattern of elevated TC prevalence similarly increased between 25 and 55 age groups and then it was steady in all provinces in 2016. Yet, there is an evident convergence in elevated TC prevalence below 40 years of age and a clear divergence in older age groups (Supplementary Figure 5).
Across provinces in 1990, age standardized prevalence for TC equal or greater than 200 in women ranged from 34·0% (28·7% – 39·6%) to 75·5% (70·0% – 78·4%), and in 2016 the range was as low as 17·8% (16·0% – 19·7%) to as high as 27·5% (24·9% – 30·2%). In men, the age standardized prevalence in 1990 ranged from 33·3% (28·6% – 38·4%) to 74·9% (71·4% – 78·2%) and in 2016, from 13·1% (11·8% – 14·6%) to 23·8% (21·4% – 26·4%) (Figure 2, Supplementary Figure 2). These measures for elevated TC are presented in supplementary figures 2 and 3.
In 1990, there were no provinces with mean TC less than 170 mg/dL in women and in 21 provinces, the mean TC was over 200 mg/dL, while in 2016 there was no province with mean TC over 200 mg/dL and in five provinces the mean TC was even less than 170 mg/dL. In men, in 1990, there were no provinces with TC less than 170 mg/dL, while in 2016 the mean TC was less than 200 mg/dL in all provinces and even less than 170 mg/dL in 22 provinces, and between 170 to 199 mg/dL in the remaining 9 provinces (Supplementary Figure 2).
In terms of raised total cholesterol prevalence, 18 provinces had decreasing percent change greater than 60% in women. While in men, 25 provinces had decreasing percent change greater than 60%. It shows that decreasing progress was more rapid in men compared to women (Supplementary Figure 6).
Figure 4 demonstrates the shift in the distribution of TC, from 1990 to 2016. This pattern shows that the mean of the entire distribution has been shifted to left; however, the standard deviation of distribution has also decreased. The decrease was more prominent in men compared to women.
In women across all provinces, the mean age standardized TC in 2016 ranged from 166·4 mg/dL (154·1 – 179·6) to 182·3 mg/dL (171·4 – 193·8). In men, respective measures for TC were as low as 159·0 mg/dL (150·1 – 168·2) to as high as 178·2 mg/dL (168·0 – 189·0) in 2016. (Supplementary Figures 1 and 2).
In terms of the trend of mean TC from 1990 to 2016, the percent decrease ranged from -23·6% (-36·3 – -8·8) to -5% (-20·1 – 13·1) in women. The equivalent results in men were -24·8% (-33·5 – -14·9) to -0·6% (-15·3 – 16·3) (Supplementary Figure 2).
For sensitivity analysis, we calculated the proportion of data points in our masked data set that were located in the 95% Uncertainty Interval of our 90 percent withheld data. For TC, 82·7 percent of 10% withheld data hold in 90% prediction of model and its uncertainty.