Thirty-Year Changes in Average Blood Lipids Levels in Populations of the Russian Federation and the USA

Aim. To conduct a comparative study of the changes in blood lipids profiles in populations of the Russian Federation (RF) and the United States of Amer-ica (USA) in different age and gender groups over the period from 1975 to 2014. Material and methods. Using a secondary analysis of data obtained from the RF population studies carried out in 1975-1982, the multicenter epidemiological study of cardiovascular diseases in different regions of the RF (ESSE-RF), conducted in 2012-2014, as well as the NHANES series of cross-sectional surveys in the civilian non-institutionalized population of the USA (NHANES II in 1976-1980 and Continuous NHANES in 2007-2012), we evaluated average lipids in blood tests in men and women of different age groups, with a total number of 48,974 observations. Results. At present, in the RF population, as compared to the USA one, most age groups demonstrate a higher concentration of total cholesterol, i.e. p<0.05 in all groups except for men aged 25-34 years (distinctions are absent) and women aged 25-34 (the concentrations are lower in Russia, p=0.05); a higher concentration of high-density lipoprotein cholesterol, i.e. p<0.005 in all men and p≤0.05 in women younger than 45 years, while in women aged 45-54 years the differences are non-significant; in 55-64-year-old women high-density lipoprotein cholesterol is higher in the USA; the concentration of triglycerides in Russia is lower in comparison with the USA in all age groups of men and women (p<0.01). Over the three decades, the total cholesterol concentration has declined in both countries; the patterns in the United States in comparison with Russia are characterized by an increase in the concentration of high-density lipoprotein cholesterol in all age groups and by the absence of a negative trend in triglyceride concentrations. Conclusion. Currently, in Russia, the total cholesterol and low-density lipoprotein cholesterol levels are worse, while triglycerides and partly high-den-sity lipoprotein cholesterol concentrations are better than in the USA. In general, the thirty-year trends for the aggregate of lipid metabolism parame-ters are better in the USA population as compared to Russia.


Changes in Blood Lipids in Russia and the USA for 30 Years
Динамика липидов крови в России и США за 30 лет Lipid metabolism disorders attract the attention of medical community more than a century, in the years since N.N. Anichkov and S.S. Khalatov. Different theories of atherogenesis have been proposed and rejected during these years, however the cholesterol theory is still the leading one. The vessel wall lesions, lipid plaques formation and cardiovascular events incidence rates were proved to increase along with increment in total cholesterol (TC) and potentially atherogenic low-density lipoprotein cholesterol (LDL-C) blood levels [1,2]. At the same time largescale international studies demonstrate that decrease in TC and LDL-C levels can prevent complications development. For example, a meta-analysis of data from 19 studies, estimated lipid-lowering drugs influence on mortality rates, revealed statistically significant decrease in coronary death relative odds by 23%, cardiovascular mortality -by 19% and in allcause mortality -by 14% [3]. The authors concluded that effective treatment is necessary both in primary and secondary coronary heart disease prevention. A more recent meta-analysis (the Cholesterol Treatment Trialists' Collaborators study), based on 27 randomized trials results, demonstrated cardiovascular risk decrease by 10 per mille for every 1 mmol/l LDL-C level reduction during 5 years [4].
At the present time the question of atherosclerosis primary prevention is debated a lot, in other words -lowering of TC and LDL-C levels in people with no signs of cardiovascular diseases [5].
Multiple risk factors promote atherosclerosis development. Estimation of changes in TC and cholesterol of different lipoprotein classes' levels in various populations over a long time, that is to say, evaluation of atherosclerosis natural history, will help forward understanding of atherogenesis and possible influence of new medical technologies, drugs and preventive interventions on it.
The aim of this study was to compare the lipids blood levels in people of different sex and age in populations of the Russian Federation (RF) and the USA in 1975-1982 and 2007-2014 years.
The data of these studies were compared with results of cross-sectional trials dealt with the civilian noninstitutionalized population of the USA: the NHANES II (1976-1980 years) and Continuous NHANES (C.NHANES, 2007-2012 years) of the National Health and Nutrition Examination Survey (NHANES) series. The studies design and methods of indices assessment had been reported in the relevant documentation provided on the National Center for Health Statistics (NCHS) of the USA Web site [9].
Age, gender, blood concentrations of TC, highdensity lipoprotein cholesterol (HDL-C), LDL-C and triglycerides (TG) were analyzed. The concentrations were compared in men and women in age groups of 25-34, 35-44, 45-54 and 55-64 years in each population study.
Statistical analysis was conducted using standard statistical methods. At the groups comparison nonparametric methods were preferred, in particular, Mann-Whitney U test was used. Mean values and standard deviations (M and SD) were also calculated.

Results and discussion
Tables 1 and 2 present results of comparison of the blood lipids indices in the populations of the RF and the USA in the end of the 2010 th years and 30 years earlier, respectively.
According to the contemporary data ( Table 1, the ESSE-RF and Continuous NHANES 2007-2012 studies) TC and LDL-C levels were higher in all groups of men and women above 34 years in the RF as compared to the USA; HDL-C levels were higher in the RF in men of all age groups and women under 45 years, at that women above 44 years revealed gradual change of the trend of HDL-C level distinctions on the inverse. Significantly lower levels of TG were reported in all groups in the RF.

Changes in Blood Lipids in Russia and the USA for 30 Years
Динамика липидов крови в России и США за 30 лет compared to the USA, distinctions in HDL-C levels in women of 45-64 years were statistically insignificant. The people of all RF groups had significantly lower TG levels except for women aged 55-64 years, they revealed insignificant distinctions however the trend was the same. So, ratios of HDL-C and TG mean values in the RF and the USA in recent years and 30 years earlier were in general the same: HDL-C levels were higher and TG levels -lower in majority of age groups in the RF as compared to the USA. TC indices had worsened in the RF as compared to the USA: while in the 80 th years of the 20 th century TC levels were lower in the RF or distinctions were insignificant, at the presentday TC levels are higher in almost all the groups.
Mean values of serum TC began to decline in the USA since at least 1960 [10][11][12]. Reducing of increased TC level, which has been observed in recent years, can most likely be explained by correction of some behavioral factors, advanced awareness of lipid metabolism disorders, improved food ration with decreased consumption of trans fats and by wider use of lipid-lowering drugs (statins) [13]. Despite these improvements, cardiovascular diseases remain the most important cause of death in the USA [14].
It should be noted that reducing of LDL-C levels continued from 2001 to 2008 years [12] but stopped in 2009 and remains unchanged up to the present [15]. This plateau was seen in groups of all ages and both genders.
Следует отметить, что снижение уровней ХС ЛПНП в США продолжалось с 2001 по 2008 гг. [12], но остановилось в 2009 г., и остается практически неизменным до на-  of all the indices as compared to the RF: HDL-C level increased in all the groups (in majority of cases in Russia the changes were negative or absent), TG level remained unchanged (increased in the RF). The above described (Table 1) advantages of the RF population as compared to the USA one (lower TG and higher HDL-C levels in majority of the groups) can be explained by significant distinctions in these indices in favor of Russia in the 80 th years of the 20 th century (Table 2), these advantages are not yet fully neutralized by a loss in the 30-year changes of the indices in comparison with the USA.

Conclusion
Consistent outputs were received in four largescale samples of two different populations -the RF and the USA (RF-1980, ESSE-RF, NHANES II and Continuous NHANES). The total number of the analyzed cases was 48,974.
Systematic distinctions have been found out between the populations of the RF and the USA. The RF population revealed worse TC and LDL-C indices, better TG and partly better HDL-C values.
Both countries have achieved reduction in TC level during the three decades, cumulative dynamics of indices was better in the USA population as compared to the RF one.

Acknowledgement
The authors express gratitude to the ESSE-RF study participants for acquisition of the RF population data, used in this article.
Besides, our study had become possible due to free access to the data of the trials of the NHANES series provided by the National Center for Health Statistics (NCHS) of the USA. The authors of the article are responsible for analysis results, interpretations and conclusions, the NCHS responsibility is limited by the primary data.
The work was conducted in the frame of the State task: "Epidemiology of cardiovascular diseases in regions of the RF (ESSE-RF-prospective). Development of the system of observation for epidemiological situation concerning cardiovascular diseases and their risk factors in the RF regions (ESSE-RF-2)", identification number АААА-А17-117070760036-6.

Changes in Blood Lipids in Russia and the USA for 30 Years
Динамика липидов крови в России и США за 30 лет