The world health report

Chapter 4

Other diet-related risk factors and physical inactivity

As well as undernutrition, substantial disease burden is also attributable to risks that are related to overconsumption of certain foods or food components. This section includes estimates of burden of disease attributable to suboptimal blood pressure, cholesterol and overweight, as well as low fruit and vegetable intake and physical inactivity (see Table 4.3). Some summary results are shown graphically in Figure 4.3a and Figure 4.3b .

High blood pressure

Blood pressure is a measure of the force that the circulating blood exerts on the walls of the main arteries. The pressure wave transmitted along the arteries with each heartbeat is easily felt as the pulse -- the highest (systolic) pressure is created by the heart contracting and the lowest (diastolic) pressure is measured as the heart fills. Raised blood pressure is almost always without symptoms. However, elevated blood pressure levels produce a variety of structural changes in the arteries that supply blood to the brain, heart, kidneys and elsewhere. In recent decades it has become increasingly clear that the risks of stroke, ischaemic heart disease, renal failure and other disease are not confined to a subset of the population with particularly high levels (hypertension), but rather continue among those with average and even below-average blood pressure (16,18) (see Figure 4.4).

The main modifiable causes of high blood pressure are diet, especially salt intake, levels of exercise, obesity, and excessive alcohol intake. As a result of the cumulative effects of these factors blood pressure usually rises steadily with age, except in societies in which salt intake is comparatively low, physical activity high and obesity largely absent. Most adults have blood pressure levels that are suboptimal for health. This is true for both economically developing and developed countries, but in the European subregions blood pressure levels are particularly high. Across WHO regions, the range between the highest and lowest age-specific mean systolic blood pressure levels is estimated at about 20 mmHg. Globally, these analyses indicate that about 62% of cerebrovascular disease and 49% of ischaemic heart disease are attributable to suboptimal blood pressure (systolic >115 mmHg), with little variation by sex.

Worldwide, high blood pressure is estimated to cause 7.1 million deaths, about 13% of the total. Since most blood pressure related deaths or nonfatal events occur in middle age or the elderly, the loss of life years comprises a smaller proportion of the global total, but is nonetheless substantial (64.3 million DALYs, or 4.4% of the total). Of this disease burden, 20% occured in WPR-B, 19% in SEAR-D and 16% in EUR-C.

High cholesterol

Cholesterol is a fat-like substance, found in the bloodstream as well as in bodily organs and nerve fibres. Most cholesterol in the body is made by the liver from a wide variety of foods, especially from saturated fats, such as those found in animal products. A diet high in saturated fat content, heredity, and various metabolic conditions such as diabetes mellitus influence an individual's level of cholesterol. Cholesterol levels usually rise steadily with age, more steeply in women, and stabilize after middle age. Mean cholesterol levels vary moderately between regions, although never more than 2.0 mmol/l in any age group.

Cholesterol is a key component in the development of atherosclerosis, the accumulation of fatty deposits on the inner lining of arteries. Mainly as a result of this, cholesterol increases the risks of ischaemic heart disease, ischaemic stroke and other vascular diseases. As with blood pressure, the risks of cholesterol are continuous and extend across almost all levels seen in different populations, even those with cholesterol levels much lower than those seen in North American and European populations.

High cholesterol is estimated to cause 18% of global cerebrovascular disease (mostly nonfatal events) and 56% of global ischaemic heart disease. Overall this amounts to about 4.4 million deaths (7.9% of total) and 40.4 million DALYs (2.8% of total). Of this total disease burden, 27% occurred in SEAR-D, 18% in EUR-C and 11% in WPR-B. In AMR-A and Europe, 5--12% of DALYs were attributable to suboptimal cholesterol levels. In most regions, the proportion of female deaths attributable to cholesterol is slightly higher than that for men.

Obesity, overweight, and high body mass

The prevalence of overweight and obesity is commonly assessed using body mass index (BMI), a height/weight formula with a strong correlation to body fat content. WHO criteria define overweight as a BMI of at least 25 kg/m2 and obesity as a BMI of at least 30 kg/m2. These markers provide common benchmarks for assessment, but the risks of disease in all populations increase progressively from BMI levels of 20--22 kg/m2.

Adult mean BMI levels of 20--23 kg/m2 are found in Africa and Asia, while levels are 25--27 kg/m2 across North America and Europe. BMI increases among middle-aged and elderly people, who are at greatest risk of health complications. Increases in free sugar and saturated fats, combined with reduced physical activity, have led to obesity rates that have risen three-fold or more since 1980 in some areas of North America, the United Kingdom, Eastern Europe, the Middle East, the Pacific Islands, Australasia and China. A new demographic transition in developing countries is producing rapid increases in BMI, particularly among the young. The affected population has increased to epidemic proportions, with more than one billion adults worldwide overweight and at least 300 million clinically obese (19).

Overweight and obesity lead to adverse metabolic effects on blood pressure, cholesterol, triglycerides and insulin resistance. Risks of coronary heart disease, ischaemic stroke and type 2 diabetes mellitus increase steadily with increasing BMI. Type 2 diabetes mellitus -- confined to older adults for most of the 20th century -- now affects obese children even before puberty. Modest weight reduction reduces blood pressure and abnormal blood cholesterol and substantially lowers risk of type 2 diabetes. Raised BMI also increases the risks of cancer of the breast, colon, prostate, endometrium, kidney and gallbladder. Although mechanisms that trigger these increased cancer risks are not fully understood, they may relate to obesity-induced hormonal changes. Chronic overweight and obesity contribute significantly to osteoarthritis, a major cause of disability in adults.

In the analyses carried out for this report, approximately 58% of diabetes mellitius globally, 21% of ischaemic heart disease and 8--42% of certain cancers were attributable to BMI above 21 kg/m2. This amounted to about 13% of deaths in EUR-B and EUR-C and 9--10% of deaths in AMR-A, AMR-B and EUR-A. High BMI causes 8--15% of DALYs in Europe and AMR-A, but less than 3% in Africa, AMR-D, South-East Asia, EMR-D and WPR-A. The proportions of DALYs caused by high BMI are slightly higher for women than for men.

Low fruit and vegetable intake

Fruit and vegetables are important components of a healthy diet. Accumulating evidence suggests that they could help prevent major diseases such as cardiovascular diseases (20) and certain cancers principally of the digestive system (21). There are several mechanisms by which these protective effects may be mediated, involving antioxidants and other micronutrients, such as flavonoids, carotenoids, vitamin C and folic acid, as well as dietary fibre. These and other substances block or suppress the action of carcinogens and, as antioxidants, prevent oxidative DNA damage.

Fruit and vegetable intake varies considerably among countries, in large part reflecting the prevailing economic, cultural and agricultural environments. The analysis assessed the levels of mean dietary intake of fruit and vegetables (excluding potatoes) in each region, measured in grams per person per day. The estimated levels varied two-fold around the world, ranging from about 189 g/day in AMR-B to 455 g/day in EUR-A.

Low intake of fruit and vegetables is estimated to cause about 19% of gastrointestinal cancer, and about 31% of ischaemic heart disease and 11% of stroke worldwide. Overall, 2.7 million (4.9%) deaths and 26.7 million (1.8%) DALYs are attributable to low fruit and vegetable intake. Of the burden attributable to low fruit and vegetable intake, about 85% was from cardiovascular diseases and 15% from cancers. About 43% of the disease burden occurred in women and 15% in EUR-C, 29% in SEAR-D and 18% in WPR-B.

Physical inactivity

Opportunities for people to be physically active exist in the four major domains of their day-to-day lives: at work (especially if the job involves manual labour); for transport (for example, walking or cycling to work); in domestic duties (for example, housework or gathering fuel); or in leisure time (for example, participating in sports or recreational activities). In this report, physical inactivity is defined as doing very little or no physical activity in any of these domains.

There is no internationally agreed definition or measure of physical activity. Therefore, a number of direct and indirect data sources and a range of survey instruments and methodologies were used to estimate activity levels in these four domains. Most data were available for leisure-time activity, with fewer direct data available on occupational activity and little direct data available for activity relating to transport and domestic tasks. Also, this report only estimates the prevalence of physical inactivity among people aged 15 years and over. The global estimate for prevalence of physical inactivity among adults is 17%, ranging from 11% to 24% across subregions. Estimates for prevalence of some but insufficient activity (<2.5 hours per week of moderate activity) ranged from 31% to 51%, with a global average of 41% across the 14 subregions.

Physical activity reduces the risk of cardiovascular disease, some cancers and type 2 diabetes. These benefits are mediated through a number of mechanisms (22). In general, physical activity improves glucose metabolism, reduces body fat and lowers blood pressure; these are the main ways in which it is thought to reduce the risk of cardiovascular diseases and diabetes. Physical activity may reduce the risk of colon cancer by effects on prostaglandins, reduced intestinal transit time, and higher antioxidant levels. Physical activity is also associated with lower risk of breast cancer, which may be the result of effects on hormonal metabolism. Participation in physical activity can improve musculoskeletal health, control body weight, and reduce symptoms of depression. The possible effects on musculoskeletal conditions such as osteoarthritis and low back pain, osteoporosis and falls, obesity, depression, anxiety and stress, as well as on prostate and other cancers are, however, not quantified here.

Overall physical inactivity was estimated to cause 1.9 million deaths and 19 million DALYs globally. Physical inactivity is estimated to cause, globally, about 10--16% of cases each of breast cancer, colon and rectal cancers and diabetes mellitus, and about 22% of ischaemic heart disease. Estimated attributable fractions are similar in men and women and are highest in AMR-B, EUR-C and WPR-B. In EUR-C, the proportion of deaths attributable to physical inactivity is 8--10%, and in AMR-A, EUR-A and EUR-B it is about 5--8%.