We can look at figures from perhaps two sources here. One is of course the global observatory in London, which was set up by the ADI some years ago. That observatory, run by Professor Martin Prince, has been collecting data, and these data were actually published by the Alzheimer's Disease International in 2015. The estimate was that there were roughly about 45 to 50 million people, I think the figure they came to was 47.8 or something like that, around the world. More recently there was another publication that’s from the Global Burden of Disease group, which is run from Washington DC. They came to very similar figure, about 45 million, so that’s really the number of people overall in the world, with a diagnosis of dementia.
我们也许可以从两个地方查找全球认知症患者的数据。其中一个当然是伦敦的全球天文台，它是由ADI在多年前建立的。Martin Prince教授一直在用这个天文台收集数据，而这些数据于2015年刊登在了国际阿尔兹海默病期刊上。该数据估计全球有4.5-5千万人被诊断为认知，我认为他们得到的数据应该大约在4.78千万左右。最近，另一份来自华盛顿的全球疾病负担小组的出版物也指出全球有4.5千万人被诊断为认知症。这个数据和之前Martin Price教授他们采集的数据（4.5-5千万）非常接近。所以，全球真的有这么多认知症患者。
But I must emphasise that this is not a precise figure, and for various reasons. One is that the data we have from many countries, is secondary data, we do not have good surveys. Even from high income countries or developed countries, the figures on dementia vary depending upon what criteria have been used, what the sampling strategy has been. This is a very rough guide.
I think there are two points I want to make here. First point is that there is an increase in the number of people, and that is quite a rapid increase projected over the next 30 to 40 years. Primarily that increase is driven by the increase in the total number of people, who are over the age of 60 or 65. We know that dementia increases exponentially with age, and especially after the age of 65, there is a doubling of the number of people with dementia. Every 6 years or 6.3 years to be precise, I think is probably the estimate. The more older people there are, the more people with dementia there will be. We know there are going to be more and more older people around the world.
In particular in the developing countries or low income countries and low and middle income countries, there is going to be a rapid increase, because those populations are ageing now. Whereas in the high income countries, the population has already aged to a significant degree. But ageing is happening very quickly in those countries. In fact they're going to contribute more and more towards people with dementia in the future. That’s really one reason that there is going to be more and more people with dementia around the world. It's projected that by the middle of the century, the number is going to be more than twice as many. One projection is maybe about 150 million people by the middle of the century around the world.
The second point I want to make is that there are some other trends we are seeing. Especially this trend has come from developed countries, high income countries, that in fact the incidence of dementia may actually not be rising, may in fact be falling. I think here we need to distinguish between the overall numbers, the prevalence of dementia, and incidence. By incidence we mean people with a new diagnosis of dementia, so how many new people are coming in to this fold of getting a diagnosis of dementia. There have been some studies from Europe and from North America, which have suggested that in fact the incidence of dementia in the developed countries may be falling, or may have been falling for the last two decades or so, and may continue to fall for some more time. Although we think that that will plateau, sometime in the future.
In particular I want to highlight three studies here. The first study perhaps, is from the UK, which is called the MRC CFAS study. Essentially it was a large study from six centres in the United Kingdom, which was done twice. Once this study was done to look at the overall prevalence of dementia in the UK in the early ‘90s. Then the study was repeated 20 years later, so to see after a generation what has happened. The short message from that study is that what they had projected was that the rate would be about 8.1% 20 years later. But actually the rate that they found on this survey, on this, was much lower, about 6.7%. There were fewer people with dementia than they had projected from the earlier estimates. In fact the total number had not gone up very much, even though the number of people who were at risk, of that old age population, had gone up significantly, suggesting that fewer people were developing dementia than 20 years earlier.
Then there’s another study from The Netherlands, that's the Rotterdam study, and the Rotterdam study is interesting because they've been following people in Rotterdam as they grow older over several years now. They looked at their rates of dementia and here they're looking at new cases, which is the incidence of dementia, 10 years apart. They found that 10 years later, the incidence was lower. Although not significantly lower, but slightly lower, not statistically significant. But a very interesting study that’s been published from the United States and that’s from a place called Framingham in Massachusetts. The audience will be familiar with the Framingham study, which actually is a study of cardiovascular health, which has been going on now for 40 to 50 years.
They started with heart health and now they've gone on to brain health. They've been looking at dementia cases now for about 40 years. They looked at rates in the late ‘70s, and then the ‘80s, ‘90s and the 2000s and see what has happened. They found that each decade, the incidence of dementia has actually gone down, to the extent that over this period of 30 years, there was about a 44% reduction in the incidence or new cases of dementia. So in fact there's both a bad news story and a good news story in this. The bad news story is that overall the number of people with dementia around the world is increasing and is likely to increase. The greatest increase is going to be in low and middle income countries. But high income countries, still there's going to be maybe an increase, but not as much as we had feared in the past. Because there is probably a levelling off or even a slight decline in these people. Unfortunately in the low and middle income countries, this decline is not likely to happen very soon, in fact at this point, there is some suggestion that the rates may be increasing to some extent because of certain risk factors.
We do not know for sure why the numbers in low and middle income countries are increasing. But definitely the major increase is because there are more older people, the life span is increasing so more people are at risk of developing dementia. So that’s the big bulk. But whether there is another contribution being made by factors such as obesity, diabetes, poor metabolic health, cardiovascular disease, stroke, we’re not sure. Because some of these are increasing, unfortunately in many low and middle income countries, with changes with industrialisation, changes in dietary patterns, changes in physical activity levels. Rates of diabetes are increasing, rates of stroke are increasing. This is happening in India, in China, which are major populations really in terms of total world population. It is possible that this will flow on through in terms of rates of dementia in the future. At this point we do not know, but that’s something that we have to watch out for.
Studies that have looked at the changes in prevalence and incidence of dementia across say a 20 year span or over a generation, have tried to hone in to the possible reasons. If you look at the Framingham study, they found that the major change was in vascular dementia, not in Alzheimer's disease, so it is suspected that it could be vascular risk factors, such as better control of hypertension, better control of diabetes, good management of cardiovascular disease. But that did not explain all of the change really.
There is a suspicion that it may be other factors, and starting off with early life factors, such as good education. We find that getting a good education early in life, sets you up for a good health lifestyle, throughout your life. It also gives you protection in terms of cognitive ageing, of decline in your cognitive function as you age. This is evidence that comes from the European studies as well and in fact even from our own study in Sydney. Early education is a significant protective factor. It may work through various different ways. But certainly better control of vascular risk factors, good diet through life, management of obesity, physical activity through life, are all important and maybe all are playing a role in this, in terms of the improvements we are seeing.
I think I should add then, that we suspect that if we are seeing an improvement in the high income countries, in the last two to three decades, we cannot take it for granted. Because it’s very likely that this will level off and then we are also seeing that in our younger populations, in developed countries, rates of obesity are increasing, and poor diet, dietary patterns are increasing as well. It’s possible that we might reverse some of these gains in the future. We cannot actually sit back on our laurels, we have to be vigilant forever.