CV mortality more common in low-income than in high-income countries

ESC 2019 The PURE study shows that in high-income countries, cancer accounts for more deaths than CVD, while in low-income countries CVD mortality is higher, although risk factors are lower there.

PURE: Impact of modifiable risk factors on cardiovascular disease and mortality

Presented at ESC Congress 2019 in Paris, France by Salim Yusuf (Hamilton, ON, Canada)

During the press conference dr. Yusuf also presented the data on modifiable risk factors, which would be presented by dr. Darryl P Leong in the main session.

Introduction and methods

The Prospective Urban Rural Epidemiology (PURE) Study collects data from a total of 202,000 participants, in 27 countries, with ongoing follow-up. 21 Countries have follow-up, and 6 countries have recently joined, so follow-up is awaited. All parts of the world, except Australia, are represented in this cohort.

These analyses of the PURE data looked into the distribution cause-specific deaths in low-income countries (LIC), middle income countries (MIC) and high income countries (HIC). Moreover, the impact of modifiable risk factors on CVD and mortality was explored for the different types of countries.

Main results

• The data show a new transition, towards CVD as a cause of death going down in HIC (23% in HIC, 42% in MIC and 43% in LIC).
• Cancer mortality rates are 15%, 30% and 55% for LIC, MIC and HIC, respectively.
• Age- and sex-standardized overall mortality rates decrease with increasing income, showing about 13 per 1000 person-years (PY) for LIC, 7 per 1000 PY for MIC and about 3 per 1000 PY for HIC. Cause-specific death rates show increasing rates with lower income for CV, respiratory, injury- and infection-related death, and a slight declining pattern for cancer death.
• The ratio of CV deaths to cancer deaths is 0.4 in HIC, 1.3 in MIC and 3.0 in LIC.
• The population attributable fraction (PAF) for CV disease shows that the most important risk factor is hypertension, followed by high non-HDL, with household air pollution on the third place. Tobacco, poor diet, low education and abdominal obesity (not BMI, Yusuf added) follow with similar PAF.
• PAF analysis for mortality shows that low education is the most important risk factor, followed by tobacco, low grip strength and poor diet, which all contribute to a similar extent.
• When specifying PAF for CV disease per type of country, it becomes clear that in HIC, behavioral and metabolic risk factors determine almost all risk. In MIC and LIC, a greater impact of low education and household air pollution is noted. PAF analysis for mortality gives a slightly different pattern, with low education also playing a role in HIC, greater impact of behavioral factors and less influence of metabolic factors for all. Low grip strength also shows some impact on mortality, mostly in MIC and LIC.

Conclusions

Based on these results, Yusuf concluded that CVD is more common in poorer countries and CVD accounts for about 40% of deaths globally (23% HIC, 42% MIC, 43% LIC). Cancer deaths are more frequent than CVD deaths in several HIC and some upper MIC. The differences in CVD rates are not primarily due to differences in metabolic risk factors, but may be due to differences in smoking, diet, air pollution and access to care.

The data are applicable to the countries involved and may not necessarily translate to other countries. It is, however, relevant to note that the cohort consists of non-selected participants.

Discussion

During the press conference, the question was raised what should be focused on in LIC and MIC in terms of CVD prevention. Greatest benefit may be expected from reducing smoking, controlling hypertension and appropriate investments in healthcare. As an example, Yusuf mentioned that some provinces in India are now investing more in healthcare, and an effect of this measure can be seen. Thus, having healthcare systems set up, low-cost drugs available, smoking cessation and control of BP and lipids helps. Moreover, it helps to train non-physician healthcare workers to focus on prevention, because they likely are more dedicated and effective at helping control risk factors than physicians.

The finding that grip strength impact mortality may be explained by that is could be a marker of frailty. That is currently being investigated in more detail. Yusuf suggested it may also be related to childhood nutrition, and protein consumption. Genomic and proteomic research to look into this is ongoing.

During the discussion it came up that the etiology of cancer is more complicated to understand than of CVD. Effects of smoking generally show a delay of 20 years. Some signs are now appearing that air pollution may also relate to cancer, and preliminary data suggest that insecticides and pesticides may also be linked to cancer. Thus, Yusuf said, we need new lines of thinking about that. Many cancers are now also related to HIV, HPV and other viruses. We begin to understand it more, but a lot remains to be elucidated.

- Our reporting is based on the information provided at the ESC congress -

Watch our video about the PURE trial

The PURE morbidity and mortality data have simultaneously been published in The Lancet The PURE risk factor data have simultaneously been published in The Lancet