Research shows that brain health is promoted by maintaining blood pressure and cholesterol in a healthy range.

Our thanks to Dr Aik Haw Tan for his help with this month's topic. Aik is a geriatrician working at Palmerston North Hospital for MidCentral DHB.

High blood pressure
  • The body needs to maintain a certain blood pressure to move blood across the circulation system.
  • Blood pressure is usually measured at the arm and is recorded as two numbers – the top “systolic” pressure just after the heart has produced a beat and the bottom “diastolic” pressure just before the next heartbeat. This is recorded in “millimetres of mercury” (or mmHg) because that’s the way blood pressure was traditionally measured.
  • A person has high blood pressure, also known as hypertension, when a blood pressure above a certain value is detected when the person is calm and at rest. This is often defined as a systolic pressure of more than 140mmHg and/or a diastolic pressure of more than 90mmHg when measured from the arm.
  • In a study done in New Zealand between 2008/2009, 31% of participants had hypertension. In the USA between 2017-2018 it was 45.4%. Males are more likely to have hypertension than females.
  • While most hypertension is diagnosed during a clinic appointment with a health professional, there is increasing awareness that some hypertension occurs mainly during sleep. This is called “masked hypertension”.
  • Hypertension is associated with an increased risk of heart attacks, heart failure, strokes and narrowing blood vessels in the limbs. These adverse outcomes become more likely if the hypertension starts at a young age and is not treated.
High blood pressure and dementia
  • In certain studies, people with severe hypertension had performed less well on tests of memory and brain power compared to those with normal blood pressure. Treating the high blood pressure improved some of the cognitive performance. However, these studies are all small and had a short follow-up time.
  • High blood pressure in people 70 years of age or less is associated with an increased risk of developing dementia later in life. Those with hypertension in mid-life, from 40-59 years, are at the highest risk of subsequently developing dementia.
  • High blood pressure can be treated using medications called “antihypertensives”. There are many types of blood pressure medications. Generally speaking, it is the amount of reduction in blood pressure that reduces the risk of complications of hypertension, not the type of drug used. However certain medical conditions that might co-exist with hypertension need specific types of medications.
  • Use of antihypertensive medications may reduce the risk of developing subsequent dementia, especially when they are prescribed for people with hypertension under 70 years of age.
  • Besides using medication, living a healthy lifestyle via moderate to vigorous aerobic exercise thirty minutes a day, eating less salt, and reducing weight helps with maintaining a healthy blood pressure. As we have seen in other topics across the year, some studies found these same healthy lifestyle changes also reduce the risk of developing dementia.
  • So for people under 70 years of age, achieving a blood pressure of less than 130/80mmHg using medication and/or lifestyle changes will likely reduce their risk of developing dementia later in life. It has been difficult to prove this conclusively in studies for various reasons but most health professionals accept that it is almost certainly true.
  • Once a person already has a dementia, studies are much less helpful to work out what to do. What is clear is that low blood pressure is also risky, and that blood pressure can gradually drop as a dementia progresses, so it may be important to reduce antihypertensive medication that was previously necessary, in consultation with a doctor or nurse practitioner.
Cholesterol
  • “Cholesterol” is not a single thing – it is a collection of different substances used to maintain the structure and function of the human body. We need a certain level of the various types of cholesterols to maintain our health.
  • These various cholesterols are present in the blood. Their levels are usually measured from a blood test done after fasting (that is, after not eating or drinking anything except water for a period of time).
  • High levels of a type called “LDL cholesterol” are associated with a increased risk of heart attacks and strokes. In the USA about 12% of those ³20 years and older have raised LDL. Not surprisingly LDL is sometimes called the “bad” cholesterol.
  • On the other hand, low levels of a type called “HDL cholesterol” is associated with a higher risk of heart attacks and strokes in some studies.
  • In most studies, lowering LDL cholesterol has been found to reduce the risk of heart attacks, however raising HDL cholesterol has not been found to consistently reduce cardiovascular risk.
  • Smoking, obesity, and a diet low in leafy vegetables, fruits, legumes (beans, chickpeas, and lentils), nuts, and dietary fibre is associated with decreased HDL levels and increased LDL levels. Regular exercise of 30 minutes a day can improve HDL levels. If regular exercise is combined with both weight loss and a diet rich in leafy vegetables, fruits, legumes, nuts, and fibre, LDL levels can be reduced.
  • A class of drugs called statins is used in the treatment of high LDL cholesterol. In those with a prior history of having a heart attack or stroke, taking a statin has been shown to reduce the risk of having a further heart attack or stroke.
High cholesterol and dementia

  • High LDL cholesterol in mid-life (40 to 65 years) is associated with a modest increased risk of developing dementia. The higher the LDL level, the greater the increase in risk.

  •  Higher HDL level in mid-life is conversely associated with a modestly reduced chance of developing dementia in later life, although not all studies find this.

  • Higher LDL cholesterol in older people who have had a stroke is also associated with an increased risk of developing dementia.
Statins, cognitive impairment and dementia
  • There have been concerns in popular media about statins causing impairment of memory and brain power.
  • While symptoms of memory loss within thirty days of starting a statin have been reported, if people then stop the medicine, this usually resolves.
  • Multiple studies have not found any evidence that statins cause long term cognitive impairment or dementia.
  • In terms of preventing dementia, some studies have found that statins prevent dementia while others detect no effect. A recent paper that summarized all the studies suggest that statin use over a relatively long period is associated with a reduced risk of developing dementia.
  • Once a person is living with a dementia, studies do not provide any clear guidance about whether statin medications are helpful. It may be that statins can be stopped at some point, in consultation with a doctor.
“Take Home” Messages:

To protect our heart and brain health, it is important for everyone from the age of 40 onwards to ask their GP to check their heart and stroke risk factors, including blood pressure and cholesterol levels. This can be done every couple of years to keep track of any changes.

  • To reduce the chance of dementia later in life, it is important to maintain a normal blood pressure of less than 140/90mmHg, especially between the ages of 40 to 70. GPs, nurse specialists or pharmacists can help monitor your blood pressure, talk about lifestyle changes that would help, and give advice on medications if required. Ideally, we aim for a BP of under 130mmHg systolic and 80mmHg diastolic in this age group.
  • To reduce the chance of dementia in later life, it is ideal to maintain a healthy cholesterol profile. If the LDL levels are high then it is worth thinking with a heath professional about how to lower this.
  • Besides helping to improve our brain health and lower the risk of dementia later in life, focusing on our heart health reduces the risk of heart attacks, heart failure, and strokes. Lifestyle factors that are important include:
    • exercising regularly for about 30 minutes a day
    • eating a diet low in salt
    • eating a diet rich in leafy vegetables, fruits, legumes, nuts and fibre
    • quitting or refraining from smoking
    • maintaining a healthy weight range.
  • It really is true that what’s good for your heart is good for your brain!