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Graphic of a cardiogram including the shape of a heart in the readout.

Cardiovascular disease is one of the leading causes of death, taking an estimated 17.9 million lives each year (World Health Organization). Of these deaths, 85% are due to heart attack, often caused by coronary heart disease, or a stroke. Although heart attacks and strokes can kill outright, more often the affected person survives but is left severely disabled for the rest of their life. NDPH researchers are using data from population-level studies to better understand the factors that increase the risk of cardiovascular disease. 

Smoking and air pollution

Smoking is one of the biggest risk factors for cardiovascular disease, for various reasons. Firstly, the chemicals in cigarettes leave sticky deposits in the walls of arteries, which can cause fatty material to accumulate. Nicotine can also raise heart rate and blood pressure, while carbon monoxide reduces the oxygen-carrying capacity of the blood. NDPH research on the Million Women Study indicates that higher smoking rates were a key reason why women from the most deprived areas of the UK had twice the risk of coronary heart disease of those from the least deprived areas.

In some rural areas of China, the use of solid fuels such as wood and coal for domestic purposes is still common. A study based on data from the China Kadoorie Biobank, found that exposure to household air pollution from using wood or coal (solid fuels) for cooking and heating significantly increased the risk of death from cardiovascular disease. Compared with people who mainly used gas or electricity (clean fuels), those who regularly cooked using solid fuels had a 20% higher risk of death from cardiovascular disease, and those who heated their homes using solid fuels had a 29% higher risk. This was after taking into account many factors, including the participants’ socio-economic status, activity level and whether they smoked or drank alcohol. Moreover, the effects of household air pollution and tobacco smoking on heart health were additive, with the risk of death from cardiovascular disease being 76% higher among smokers who used solid fuel for cooking, compared with non-smokers who used clean fuels.

Cholesterol

High levels of blood cholesterol, particularly of the low-density lipoprotein (LDL) type, are a key risk factor for cardiovascular disease. Statins are drugs that effectively lower blood LDL-cholesterol levels, and randomised trials have shown that reducing LDL cholesterol through statin therapy significantly reduced the risk of heart attacks and strokes. In rare cases, statin therapy can result in serious muscle problems known as myopathy and rhabdomyolysis, but the benefits of statins are thought to clearly outweigh any potential adverse effects. Statins are very commonly prescribed, and are taken worldwide by millions of people.

Recent debate about whether statins may cause other adverse effects, such as less serious forms of muscle pain, has led to many patients at high risk of cardiovascular disease stopping (or not starting) statin therapy. The Cholesterol Treatment Trialists’ (CTT) collaboration, led by NDPH, is using data from large, high-quality clinical trials involving tens of thousands of patients to generate the most robust evidence possible on the nature and magnitude of any other statin effects. The preliminary results of this work are expected later in 2021. 

Read more: Statin therapy reduces cardiovascular disease risk in older people,
Statin treatment reduces the risk of cardiovascular disease in women.

High blood pressure

High blood pressure (hypertension) significantly increases the risk of cardiovascular disease, yet millions of people across the world who have the condition remain undiagnosed. An analysis of the China Kadoorie Biobank found that one third of the participants had hypertension, but of these only one third were diagnosed and less than 5% had their hypertension properly controlled. Ultimately, uncontrolled hypertension may cause 750,000 deaths in China each year from heart attacks and stroke. Similarly, an NDPH-led study on 150,000 Cuban adults found that a third of these had hypertension, of whom two-thirds had been previously diagnosed. Just over three quarters of those with diagnosed hypertension were being treated, however blood pressure was controlled in just a third of these. Uncontrolled hypertension was associated with an approximate doubling in risk of cardiovascular death and accounted for around 20% of premature cardiovascular deaths. These studies suggest that in resource-limited countries, public health measures to diagnose and treat hypertension could be an effective strategy to reduce the burden of cardiovascular disease, especially if focused on those at high absolute risk of cardiovascular death, such as those who have already had a heart attack or stroke.

Read more: BMI, blood pressure and cause-specific mortality in India: a prospective study of 500 000 adults

Exercise

It’s often said that if exercise were a pill, we would all be prescribed it, and it is certainly a factor in keeping our hearts healthy. The Million Women Study found that middle-aged women who did strenuous physical activity (enough to cause sweating or a fast heartbeat) two to three times per week, or any activity up to four to six times per week, had around a 20% lower risk of coronary heart disease, stroke and blood clots, compared to women who were inactive. Even small increases in daily activity seem to help: a China Kadoorie Biobank study found that every additional hour of brisk walking or cycling led to a 9% lower risk of heart attack, 5% lower risk of stroke and 12% lower risk of death from cardiovascular disease. Physical activity is thought to benefit cardiovascular health through several mechanisms, including strengthening the heart muscle, reducing blood pressure, improving blood sugar regulation and reducing the hardening of arteries. 

But is more exercise always better or do these benefits have a limit? Recent research by NDPH suggests that for optimum heart health, we should aim to be as active as possible. This study used wrist-worn accelerometers to record the activity of 90,000 UK Biobank participants, then followed them up over five years. The results clearly showed that higher amounts of physical activity were steadily associated with lower risk of cardiovascular disease, with no apparent threshold at high levels of activity. For those in the top quarter of total physical activity, the protective effect was estimated to be 48%-57%, and this rose to 54%-63% for vigorous-intensity activities. The association remained strong even when factors such as smoking and obesity were taken into account.

Middle-aged woman running.

Obesity

Obesity has been strongly associated with cardiovascular disease, but it is difficult to assess whether it is a direct cause as it is typically linked with other factors that can affect heart health. To address this problem, NDPH researchers have used approaches that calculate a person’s body mass index (BMI) through their genetics. In one study on the UK Biobank cohort, each participant was given a genetic risk score for obesity based on 29 genomic regions associated with BMI. The results showed a strong association between higher BMI and an increased risk of both coronary heart disease and hypertension. This is supported from observational analyses of the Million Women Study which found that coronary heart disease risk increased progressively with BMI. Women with a BMI of 21 kg/m2 had a risk of 1 in 11 between the ages of 55 and 74 years, compared with a risk of 1 in 6 for those with a BMI of 34 kg/m2. In fact, every 10 kg/m2 increase in BMI raised the risk for coronary heart disease to a similar amount as a five-year increase in age. Furthermore, a larger waist circumference was independently associated with greater risk of coronary heart disease. For women with a waist circumference of less than 70 cm, 1 in 14 developed coronary heart disease between the ages of 55 and 74 years, compared with 1 in 8 women with a waist circumference greater than 80 cm.  

Diet

Research led by NDPH indicates that excess meat consumption – particularly red and processed meat – can increase the risk of cardiovascular disease. A study on 2,820 cases of coronary heart disease in the Oxford cohort of the European Prospective Investigation Into Cancer and Nutrition (EPIC) study, for instance, indicated that pescatarians (who eats fish, but no other types of meat) and vegetarians had, respectively, 13% and 22% lower rates of coronary heart disease than meat eaters. This difference is equivalent to 10 fewer cases of coronary heart disease in vegetarians than in meat eaters per 1000 people over 10 years. Similarly, a study on the Pan-European EPIC Cohort suggested that coronary heart disease risk was positively associated with the participant’s consumption of red and processed meat: a 100g per day increase in intake appeared to raise an individual’s risk by 19%. Vegetarian, vegan and low meat diets may protect the heart through reducing intake of saturated fatty acids, improving cholesterol levels, and lowering blood pressure.

NDPH research on participants in the China Kadoorie Biobank study found that the risk of heart attack or stroke was a third higher for those who rarely ate fresh fruit, compared with those who ate it most days. It is not yet clear whether higher intakes of fruit directly reduce the risk of cardiovascular disease, or if low fruit consumption is linked with other causal factors, such as smoking. However, both fruit and vegetables are good sources of fibre, and numerous studies have shown high fibre intake to be associated with reduced risk of heart attack or stroke: for instance, data from the Pan-European EPIC study showed that every additional 10g intake of fibre a day was associated with a 23% lower risk of ischaemic stroke. It has also been suggested that fruits with a high potassium content, such as bananas, may help prevent arteries from hardening.

Read more: Fish oil supplements may not protect against heart disease

Alcohol

Excessive alcohol consumption can raise blood pressure, cause weight gain and increase the risk of heart arrhythmias, all of which can damage cardiovascular health. There is a popular belief, however, that moderate alcohol consumption can have a protective effect on the heart. This is difficult to assess reliably in observational studies, since low- or non-alcohol drinkers may abstain from alcohol due to underlying health issues. NDPH researchers used a genetic approach called ‘Mendelian randomisation’ in the China Kadoorie Biobank participants. This studied common genetic variants that are present only in East Asian populations and which greatly reduce alcohol tolerability, and therefore alcohol intake. The results showed that for men (few Chinese women drank alcohol), moderate alcohol drinking (one-two drinks per day) increased the risk of having a stroke by about 12%. Moderate drinking had no protective or harmful effects for heart attack, but further work involving a much larger number of cases is needed to confirm this.

Pregnancy and breast feeding

Research from NDPH’s National Perinatal Mortality Unit has demonstrated that, over recent years, cardiovascular disease has been the leading cause of maternal deaths, accounting for 23% of women who died during pregnancy or up to six weeks afterwards. Three quarters of the women studied did not know that they had cardiovascular disease. Pregnancy places additional strain on the heart, but in many cases cardiovascular disease symptoms were not recognised and were thought to be general symptoms of pregnancy. Women preparing for pregnancy should know the symptoms to watch out for, and ensure they are aware of their family history of cardiovascular disease.

Breastfeeding may protect new mothers from heart attacks and strokes in later life. A China Kadoorie Biobank study found that mothers who breastfed their babies had a 9% lower risk of coronary heart disease and an 8% lower risk of stroke, compared with women who did not breastfeed their babies. This protective association increased with duration of breastfeeding, so that mothers who breastfed each of their babies for two years or more had an 18% lower risk of coronary heart disease and a 17% lower risk of stroke. Although the cause-effect association cannot be established, it may be that breastfeeding helps to ‘reset’ the metabolic changes that occur during pregnancy, and deplete the fat stores that accumulate to support foetal growth.

Read more: Women’s age at first menstrual cycle linked to heart disease risk