Under Pressure: High Blood Pressure Risks In Post-Menopausal Women
High blood pressure, or hypertension, is one of the biggest risk factors for cardiovascular disease. While it affects both women and men, there are differences in when and why women and men develop hypertension.
Dr. Paula Harvey, director of the cardiac research program at Women’s College Hospital and a scientist at Women’s College Research Institute in Toronto, explored those sex differences and some of the mechanisms behind them at a presentation she gave at Women’s College Hospital on Feb. 3, 2010.
‘Hypertension is probably the most important cardiovascular risk factor in post-menopausal women,’ Dr. Harvey said. ‘Cardiovascular disease remains the leading cause of illness and death in women. And that’s the leading cause over all the next six leading causes of death and morbidity combined. So it’s a major problem.’
In younger people, blood pressure tends to be higher in men than in women. Starting around age 30, men’s blood pressure tends to gradually increase at a regular pace until about age 55. In that same age range, women’s blood pressure increases more slowly until they reach peri-menopause. That slow increase in blood pressure begins to speed up around the menopausal transition, and women’s blood pressure rises at a steeper rate as they get older.
So while hypertension is more common in young men than young women, high blood pressure rates in women begin to catch up to men in middle age.
‘And when you get into the older age group, women not only catch up, they overtake men,’ Dr. Harvey said. ‘So women have more high blood pressure than men once you get over 60 years of age.’
The many roles of estrogen
One mechanism for these sex differences in blood pressure patterns may be estrogen. In the complex interactions of the human body, estrogen plays many roles. Dr. Harvey explained how some of them may help protect premenopausal women from hypertension:
- Estrogen increases levels of nitric oxide, which is a very powerful dilator of blood vessels, and dilated blood vessels are conducive to healthy blood pressure.
- Estrogen not only helps keep blood vessels dilated by increasing nitric oxide levels, it also helps reduce levels of endothelin, a substance that constricts blood vessels and is closely linked to heart disease and high blood pressure.
- By increasing elastin and collagen, estrogen helps blood vessels maintain healthy, flexible walls.
- Estrogen’s antioxidant properties also reduce the type of free radicals called reactive oxygen species. These free radicals are implicated in cell damage and inflammatory responses, including those associated with cardiovascular disease.
- It may help reduce sodium sensitivity, making women less sensitive to the hypertensive effects of salt.
- Estrogen helps to suppress the renin-angiotensin system (RAS) that controls enzymes and hormones that affect vasoconstriction (constriction of blood vessels) and sodium retention.
- Estrogen helps to suppress the RAS’s production of angiotensin 2, a substance that triggers the sympathetic nervous system, which in turn is responsible for the fight-or-flight response that constricts blood vessels, increases heart rate and raises blood pressure.
‘Although angiotensin II was very protective back in the day, when we needed to be able to run away from tigers and lions and survive trauma, it’s not a great situation in our present lifestyle,’ Dr. Harvey said.
Given the many protective effects of estrogen, it’s not surprising that researchers suspect that estrogen deficiency following menopause is one of the contributing factors to the increase in hypertension that often occurs in post-menopausal women.
‘What we’re doing is reversing all those benefits of estrogen we see in the premenopausal period,’ Dr. Harvey said. Nitric oxide decreases, endothelin increases, blood vessel walls begin to stiffen and oxidative stress increases.
Lifestyle and hypertension
Loss of estrogen isn’t the whole story in post-menopausal hypertension. Some of the biggest risk factors are modifiable.
Studies have linked hypertension risk to body mass index (BMI) and waist-to-hip ratio – the ratio of how much fat you carry around your waist to how much fat you carry around your hips. Either – or both – of these factors can affect blood pressure.
‘As you increase your body mass index, your risk of hypertension increases,’ Dr. Harvey said. ‘As you increase the amount of fat around your waist, affecting your waist-to-hip ratio, your risk of hypertension increases. Combine the two, and you’re really in big trouble.’
The double whammy of elevated BMI and belly fat adds up to a seven-fold increase in risk of hypertension, compared to women with a normal BMI and waist-to-hip ratio.
Obesity is also big contributor. Women are more likely to be overweight than men, and this trend increases with age, Dr. Harvey said.
‘Obesity is bad,’ she said. ‘In physiological terms, it leads to all sorts of things like activation of the sympathetic nervous system, sodium retention, and it does contribute to hypertension.’
Obesity in women peaks around ages 55 to 59. Its prevalence is highest in aboriginal women, and in low-income groups.
Conversely, a healthy diet and an active lifestyle – two factors that help control BMI, obesity and waist fat – can be protective against high blood pressure.
Some specific nutrients associated with reducing risk of hypertension include calcium and magnesium. Diet elements that increase risk include alcohol, salt and cola drinks, Dr. Harvey said.
Exercise is one of the most important factors in reducing risk of high blood pressure. However, Dr. Harvey noted that 60 per cent of Canadian women are inactive, and only 17 per cent are classified as active.
‘Not surprisingly, this correlates with body mass index: the more active you are, the lower your BMI,’ she said.
Among the cardiovascular benefits of exercise is an increase in the production of nitric oxide – the substance that dilates blood vessels and helps them stay healthy.
Dr. Harvey cited a 1997 study in which post-menopausal women with high blood pressure did a 12-week treadmill exercise program. At the end of program, their blood pressure was significantly reduced. Their systolic pressure dropped by an average of 10 mmHg during the study period.
‘This is easily as good as adding a medication to somebody’s blood pressure treatment,’ Dr. Harvey said of the results.
‘We know that exercise improves your cardiovascular risk profile in a number of ways: augments the health of blood vessels, reduces blood pressure and pulse pressure,’ Dr. Harvey said. Exercise also reduces risk of cardiovascular illness and death, and actually reduces risk of death from all causes, she added.
Cardiovascular disease is already the number 1 cause of illness and death for women, and hypertension is a major risk factor that is most prevalent in post-menopausal women. Demographics will soon make these figures even more worrying.
‘It’s estimated that by 2050, there will be 1 billion women over the age of 65 in the world,’ Dr. Harvey said. ‘That’s a big cardiovascular burden.’