BMJ  2005;331:187-188 (23 July), doi:10.1136/bmj.331.7510.187

Paper

Changes in dietary fat and declining coronary heart disease in Poland: population based study

¹ Cancer Centre and Institute of Oncology, 5 Roentgena Str, 02-781 Warsaw, Poland, ² Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA

Introduction

We previously described a rapid decline in mortality due to coronary heart disease in Poland between 1991 and 1994, corresponding with increases in the ratio of polyunsaturated fat to saturated fat in people's diet and fruit consumption.¹ The changes in food consumption followed changes in economic policy, including reductions in subsidies for dairy and other animal fats. We describe subsequent trends and use data from cohort studies to estimate the contributions from smoking and diet to these changes.

Methods and results

Mortality due to coronary heart disease has continued to fall in Poland in both sexes and across educational levels. Compared with 1990, by 2002 for the age band 45-64 years it had fallen by 38% in men (340 per 100 000 to 212/100 000) and by 42% in women (76/100 000 to 44/100 000). By 1999 (the latest year with comparable data), consumption of saturated fat had fallen by 7% (44.8 g/day to 41.5 g/day), consumption of polyunsaturated fat had risen by 57% (14.8 g/day to 23.3 g/day), and the ratio of the two had increased by 70%. Per head, consumption of imported fruit rose from 2.8 kg/year in 1990 to 8.8 kg/year in 1991 and 10.4 kg/year in 1999.

From 1990 to 2004, the prevalence of smoking in Poland fell among people younger than 40 but increased from 23.1% to 35.2% among women aged 40-60. Among men, it fell from 51.1% to 46.1% at age 40-49, from 51.1% to 46.1% at 50-59, and from 34.3% to 28.2% over 60. If we assume a relative risk of 3 for current smoking then a reduction in prevalence of 5% (from 55% to 50%) would reduce the risk of coronary heart disease by about 5%. This, and similar declines in rates of coronary heart disease among men and women, indicates that changes in smoking contributed little to falling rates of coronary heart disease.

In the prospective nurses' health study, the ratio of dietary saturated and unsaturated fats was inversely related to the incidence of coronary heart disease.² The change in coronary mortality in Poland was similar to that predicted by the slope relating this ratio to the risk of coronary heart disease in the study (figure). The increased consumption of imported fruit between 1990 and 1999 corresponds to a quarter of a serving per day. In the nurses' health study and a companion cohort in men, the relative risk was 0.94 for an increase of one serving of fruit per day, which would predict a reduction of only 1-2%.³

View larger version (29K): [in this window] [in a new window]   Ratio of dietary polyunsaturated to saturated fat and mortality due to coronary heart disease in Poland (relative to rates in 1990), superimposed on the relation between the fat ratio and coronary risk observed in the nurses' health study. Changes in dietary polyunsaturated to saturated fat in Poland between 1990 and 1999 are predicted to result in a 24% drop in coronary mortality, which is similar to the observed decline

 

Comment

The experience of Poland is consistent with epidemiological and clinical evidence⁴ indicating that mortality due to coronary heart disease can be reduced by partly replacing dietary saturated fats with polyunsaturated fats while maintaining a low intake of trans fatty acids.

Polyunsaturated fat reduces serum concentrations of low density cholesterol,⁴ but this cannot account for the size and rapidity of changes in coronary mortality in Poland. A higher intake of polyunsaturated fat also improves endothelial function, reduces platelet aggregability, and reduces ventricular fibrillation.⁴ The net effect can therefore be appreciated only by evaluating coronary end points. Increased intakes of polyunsaturated fat also probably explain most of the major declines in coronary mortality in the United States, United Kingdom, and Australia over several decades.⁵

Both omega 3 fatty acids and omega 6 fatty acids seem to contribute to reductions in coronary risk.⁴ According to statistics from the United Nations Food and Agricultural Organisation,^{w1 w2} the increase in polyunsaturated fat in Poland during the 1990s was primarily from rapeseed and to a lesser degree from soya bean oil; intake of omega 3 and omega 6 fatty acid would therefore have increased, making it difficult to distinguish their relative contributions to the drop in mortality. Statistics from the Food and Agricultural Organisation do not consider changes during processing; but a conscious effort was made in Poland to minimise the trans fat content of margarines made from these oils.

What is already known on this topic Mortality due to coronary heart disease fell drastically in Poland between 1990 and 1994 What this study adds This decline has continued through 2002, with most of the decline probably resulting from a large increase in consumption of non-hydrogenated rapeseed and soya bean oil, rather than from reductions in smoking and an increase in fruit intake

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Two additional references (w1 and w2) are on bmj.com

Contributors: Both authors contributed equally to this report and are joint guarantors.

Funding: Part funding from Health Evolution Monitoring—Closing the Gap—Reducing Premature Mortality. Baseline for Monitoring Health Evolution Following Enlargement (European Union Grant Agreement No. 2003121).

Competing interests: None declared.

Ethical approval: Not needed.

References

1. Zatonski WA, McMichael AJ, Powles JW. Ecological study of reasons for sharp decline in mortality from ischaemic heart disease in Poland since 1991. BMJ 1998;316: 1047-51.[Abstract]
2. Hu FB, Stampfer MJ, Manson JE, Ascherio A, Colditz GA, Speizer FE, et al. Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women. Am J Clin Nutr 1999;70: 1001-8.[Abstract/Free Full Text]
3. Joshipura KJ, Hu FB, Manson JE, Stampfer MJ, Rimm EB, Speizer FE, et al. The effect of fruit and vegetable intake on risk of coronary heart disease. Ann Intern Med 2001;134: 1106-14.[Abstract/Free Full Text]
4. Hu FB, Willett WC. Optimal diets for prevention of coronary heart disease. JAMA 2002;288: 2569-78.[Abstract/Free Full Text]
5. Dwyer T, Hetzel BS. A comparison of trends of coronary heart disease mortality in Australia, USA, and England and Wales with reference to three major risk factors—hypertension, cigarette smoking and diet. Int J Epidemiol 1980;9: 65-71.[Abstract/Free Full Text]

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