Are heart and brain health linked?

We increasingly hear that what’s good for the heart is good for the brain. As part of our Staying Sharp series, Professor Kaarin Anstey of the Australian National University describes evidence pointing that way.

Brain health and heart health are linked

In my research team, we have examined the evidence on factors that affect our blood vessels and heart health and shown that they also affect brain health.

This isn’t surprising as the brain contains hundreds of blood vessels. Anything that causes damage to these blood vessels may also affect the cells and connections in the brain that we need for memory, thinking, and other functions.

We evaluated the link between heart health and brain health in two ways.

1. We studied a group of 2,500 people aged 60-64 years for twelve years to see what factors predicted those who developed cognitive decline and dementia (these are termed “risk factors”). We then tracked them to see who developed cognitive decline and impairment and whose brains were ageing more rapidly.
2. We collated all the results from studies like ours to get a view of the evidence overall (this is known as a meta-analysis). This approach gives us a very reliable estimate of the impact of a risk factor because it is averaged across the tens of thousands of people who took part in all the studies put together.

What matters to brain health?

The specific cardiovascular risk factors that affect brain health according to our study and the other studies we reviewed are these:

Type 1 and type 2 diabetes have both been shown to increase the risk of decline in our thinking skills in mid-life (age 40 onwards) and late-life. As well as changes to large blood vessels, diabetes can lead to complications in tiny blood vessels in the brain. This increases the impact of Alzheimer’s disease and the risk of vascular dementia. These are the two most common forms of dementia.

In middle-aged people, high cholesterol has been linked to an increased risk of developing Alzheimer's disease in later life, but not vascular dementia. At present, we are limited in what we know about the impact of cholesterol on thinking skills as we grow older because there are few studies that report consistent findings. The results we do have use the total cholesterol reading you get after fasting, rather than one of the subtypes of cholesterol. They are also drawn from very few countries. In people in late-life (e.g. 65+), we can’t find a link between high cholesterol and dementia risk, but high cholesterol has other negative effects on health and so should be avoided anyway.

Obesity in our study was associated with faster than normal shrinkage of the brain, particularly the part of the brain linked to memory. Our meta-analysis of all the studies like ours also showed that middle-aged overweight and obese people had an increased risk of dementia when they live into old age. We don’t fully understand the mechanisms for this, but some researchers have suggested it is due to excess fat around the abdomen (stomach) causing the body’s immune system to start attacking normal cells that it otherwise wouldn’t.

High blood pressure is another risk factor that impacts on our blood vessels and brain. We know that high blood pressure (hypertension) can cause a stroke, abnormal bleeding from tiny blood vessels in the brain and some changes to the white matter in the brain (the brain’s connections). Studies show that high blood pressure in middle-aged people seems to increase the risk of developing dementia in late life. In older adults the situation gets complicated and the link between high blood pressure and dementia is less clear.

Overall - a complex picture

As this summary shows, things are not always straightforward! 

It turns out – based on the evidence we reviewed – that cardiovascular risk factors in middle-aged people are much worse for brain health than the same factors when they occur in older people.

At the moment, we don’t understand why middle-age is so important. It may be that this is when the process is triggered that leads to the accumulation in the brain of a protein called amyloid-B that causes Alzheimer’s disease. Or it may be that hormonal factors are involved, or that having a risk factor in middle age simply means you are exposed to that risk factor for a longer time and so you are more likely to experience the consequences.

Whatever the explanation, it’s clear that the risk factors that compromise our cardiovascular health also compromise our thinking skills and brain health. It follows that looking after our heart health means we will also be protecting our brain health.

Key references

• Anstey, K.J., Eramudugolla, R., Hosking, D.E., Lautenschlager, N.T. and Dixon, R.A., 2015. Bridging the translation gap: from dementia risk assessment to advice on risk reduction. The Journal of Prevention of Alzheimer's disease, 2(3), p.189.
• Gardener, H., Wright, C.B., Rundek, T. and Sacco, R.L., 2015. Brain health and shared risk factors for dementia and stroke. Nature Reviews Neurology. 11, p.651–657.