In a series of animal experiments, researchers attempted to see whether high blood glucose could be involved in the development of amyloid protein plaques in the brain; a characteristic hallmark of Alzheimer’s disease. These plaques are abnormal "clumps" of protein that are thought to gradually destroy healthy brain cells.

Some studies have suggested that people with high blood glucose levels and those with type 2 diabetes may be at greater risk of the disease, and this study aimed to see why that might be the case.

The experiments found that giving the mice a sugar solution over a number of hours led to an increased concentration of amyloid in the fluid surrounding the brain cells. The effect was more pronounced in older mice.

The study has only looked at the short-term effects, and not at whether high glucose levels affected longer-term plaque formation or symptoms in the mice.

At this stage, it is not conclusively proven that type 2 diabetes is a risk factor for Alzheimer’s disease, or that you have increased risk of the disease if you have a high-sugar diet.

However, sticking to current healthy eating and activity recommendations is a good way to increase your chances of staying healthy.

Where did the story come from?

The study was carried out by researchers from Knight Alzheimer’s Disease Research Center and Washington University School of Medicine in the US, and was funded by the National Institutes of Health. The study was published in the peer-reviewed Journal of Clinical Investigation. It is an open-access study, so it is free to read online or download as a PDF.

The Daily Express accurately describes the methods of the study, but doesn’t make it clear until later in the research that study was on mice. The Daily Telegraph was more upfront about this fact.

The Telegraph piece also includes information on a related study into green tea and Alzheimer’s disease. We have not analysed the study, so we cannot say how accurate the Telegraph’s reporting of this study was.

What kind of research was this?

This was animal research that aimed to look into why there might be a link between blood glucose and risk of dementia, specifically Alzheimer’s disease.

The causes of Alzheimer’s disease are still not fully understood. Increasing age is the most well-established factor to date, and there is the possibility of hereditary factors. The influence of health and lifestyle factors is uncertain. Some previous studies have suggested that glucose levels in the blood may have an impact on the development of the beta-amyloid "plaques" and the tau protein "tangles" in the brain that are the hallmarks of the disease. This is supported by other studies that have suggested people with type 2 diabetes are more likely to develop Alzheimer’s disease. Therefore, this research aimed to look at whether there was a biological reason for this. 

Animal studies can provide a valuable indication of how disease processes may work, but the process may not be exactly the same in humans.

What did the research involve?

The researchers carried out experiments to control the blood glucose level of a genetically engineered mouse model of Alzheimer’s disease and looked at the effect on the composition of the fluid surrounding the brain cells.

The research involved three-month-old mice, who would normally be too young to have beta-amyloid protein deposits in the brain. Under anaesthetic, the researchers gained access to the large vein and artery in the neck, and then a catheter was guided through the blood vessel into one region of the brain (the hippocampus). Once the mice were awake again, these tubes allowed the researchers to infuse glucose into the brain, and to sample the fluid around the brain cells while the mice were still awake and moving around.

In their experiments, the researchers withheld food from the mice for several hours before a glucose solution was gradually infused into the brain over four hours.

Fluid around the brain cells was sampled every hour during the infusion to look at levels of glucose, beta-amyloid protein and lactate (a compound involved with the metabolism of the brain) – the latter was used as a marker of brain cell activity. The brain was also examined after death.

Other experiments included infusing older, 18-month-old, mice that would already be expected to have some beta-amyloid build-up.

They also tried infusing different drugs to examine in more depth precisely what biological mechanisms were occurring in the brain that could be causing these effects.

What were the basic results?

In the main experiments in younger mice, the glucose infusion almost doubled glucose concentration in the brain fluid and increased the concentration of beta-amyloid by 25%. Lactate levels also increased, suggesting an increase in brain cell activity.

In the older mice, glucose infusion raised the concentration of beta-amyloid even higher – by around 45%.

How did the researchers interpret the results?

The researchers found that increased blood glucose levels affect brain cell activity glucose, leading to increased beta-amyloid in the fluid surrounding the brain cells in young mice that would normally have minimal beta-amyloid. In aged mice, the effect was even more pronounced.

They further suggest that "during the preclinical period of Alzheimer’s disease, while individuals are cognitively normal, our findings suggest that repeated episodes of transient [high blood glucose], such as those found in [type 2 diabetes], could both initiate and accelerate plaque accumulation".

Conclusion

This animal study supports the theory that elevated blood sugar might influence the development of beta-amyloid plaques in the brain – one of the characteristic hallmarks of Alzheimer’s disease. As the researchers say, glucose could similarly be involved in their development in humans.

However, at this stage, we cannot extrapolate these short-term results in mice much further. While animal studies provide a valuable indication of how disease processes may work in humans, the process may not be exactly the same. The study has not looked at the long-term effects of raised glucose on plaque formation in these Alzheimer’s-model mice, and how long raised levels need to be present to have an effect.

Even if the development of amyloid plaques in the human brain could be affected by levels of glucose, we don’t understand the intricacies of how this might happen or whether it can be avoided. Body cells – particularly those in the brain – need glucose, so clearly it cannot be avoided.

Currently, it has not been conclusively proven that type 2 diabetes is a risk factor for Alzheimer’s disease, or that you have increased risk of disease development by having a high-sugar diet. However, high-calorie diets are well established to be a risk factor for overweight and obesity, which are linked to many chronic health conditions, including type 2 diabetes. Sticking to current diet and activity recommendations can help to maintain good health.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Links To The Headlines

Could cake and chocolate lead to Alzheimer's disease? The Daily Telegraph, May 6 2015

Got a sweet tooth? It could put you at risk of Alzheimer's. Daily Express, May 6 2015

Links To Science

Macauley SL, Stanley M, Caesar EE, et al. Hyperglycemia modulates extracellular amyloid-β concentrations and neuronal activity in vivo. The Journal of Clinical Investigation. Published online May 4 2015

"Third of overweight teenagers think they are right size, study shows," The Guardian says in one of many headlines on widely covered UK research.

The research, which looked into English 13-15-year-olds' understanding of their own weight, led the Mail Online to refer unkindly to "generation fat-blind".

The large study demonstrated that while most normal-weight adolescents correctly see themselves as about the right weight, a large number of overweight or obese adolescents wrongly thought they were about the right weight or too light.

Parents probably ought to refrain from a "told you so" attitude to this news, as so-called fat shaming is not considered a great way to help anyone lose weight.

Helping a teen to understand that familiar media images of overweight and obese people don't necessarily give the full picture, and that addressing the problem can improve the quality and length of their life, may be more successful.

The findings may also help policymakers work out how best to target health promotion messages at this important age group and help them potentially make changes for the rest of their lives. 

Where did the story come from?

The study was carried out by researchers from University College London and was funded by Cancer Research UK.

It was published on an open-access basis in the peer-reviewed International Journal of Obesity.

This study was accurately reported by a number of media sources, with a good explanation of its key findings and the risks associated with obesity.

However, there was a general lack of information about the limitations of this study. The Mail's headline use of the term "fat-blind" may be seen as pejorative and misleading, especially when we do not necessarily understand all the reasons for the research findings. 

What kind of research was this?

This study analysed data from the Health Survey for England looking at adolescents' perception of their weight.

Looking at this data is a good way to understand adolescents' weight perceptions because measurements were taken professionally and weight perception questions were self-reported in the survey.

However, this type of study can have chunks of missing data, particularly where people declined to be weighed, which may have biased the results. 

What did the research involve?

The researchers used data for 4,979 teens aged 13 to 15. The data was taken from the results of the Health Survey for England between 2005 and 2012.

This annual survey presents a representative sample of the general population of England. It surveys adults and up to two children under 16 (selected at random in families with three or more eligible children).

Researchers weighed and measured the teens at home, and then calculated their body mass index (BMI). Weight status was defined according to the International Obesity Taskforce criteria, which classifies BMI values according to age and sex as:

• thin (underweight)
• normal weight
• overweight
• obese

The 13-15-year-olds were also asked: "Given your age and height, would you say that you are about the right weight, too heavy, or too light?".

The researchers also included age, sex, ethnicity and the socioeconomic status of the teens in their analyses. 

What were the basic results?

The data showed nearly three-quarters (73%) of adolescents in the study had a BMI placing them in the normal weight range, but 20% were overweight and 7% were obese.

Normal-weight adolescents generally felt they were the correct weight (83%), with just 7% who thought they were too heavy, while 10% thought they were too light.

More girls (11%) considered themselves too heavy than boys (4%). Girls (6%) were also less likely to consider themselves too light than boys (13%).

Overestimation was more likely among those on the heavier end of the normal-weight group (10%) than the lighter end (2%).

About 60% of the overweight/obese group felt they were too heavy, 39% thought they were about the right weight, and 0.4% felt they were too light.

Again, girls (68%) who were overweight or obese were more likely to think so than boys (53%).

Girls (32%) were also less likely than boys (47%) to think they were the right weight or too light. Overweight adolescents were much more likely to underestimate their weight (52%) than those who were obese (7%).

The researchers excluded adolescents who were underweight from the analysis as this group consisted of 248 people, which they say was too small to calculate meaningful results. 

How did the researchers interpret the results?

The researchers concluded that, "Overestimation of body weight among normal-weight adolescents is relatively uncommon; potentially a cause for celebration.

"However, almost half of boys and a third of girls with a BMI placing them in the overweight or obese BMI range perceived themselves to be about the right weight.

"Lack of awareness of excess weight among overweight and obese adolescents could be cause for concern." 

Conclusion

This study aimed to see whether UK teenagers' perception of their weight matched up with reality. It demonstrated that most normal-weight adolescents correctly see themselves as about the right weight and they overestimated their weight fairly rarely.

But a large proportion of overweight and obese adolescents thought they were about the right weight or even too light.

This study had a large population size, and analyses were weighted to match key population characteristics.

However, the weight measurements were not available for all adolescents in the survey – this may have represented those who were more concerned about their weight and declined measurement, leading to biased results.

Also, overweight and obese adolescents may not have completed the questionnaires truthfully through embarrassment or fear of the consequences.

Only people aged 13 to 15 were analysed, so further research would need to be carried out in other age groups to target issues associated with weight perception if necessary.

Overweight and underweight teens are a concern to both their parents and society. They are likely to grow into overweight or underweight adults, particularly if they do not see that they are not a healthy weight.

The reasons teenagers don't see themselves as overweight may include the commonly seen images of severely obese individuals in the media used to represent stories about weight issues. These could lead to the impression that only those who have a visibly very high body weight are overweight or obese.

Excess weight can lead to a range of other health concerns, including an increased risk of type two diabetes and certain cancers.

Even if teenagers aren't interested in these long-term health messages, it's vital to find ways to improve their understanding of the implications of their weight. And if they understand, it's vital we're able to give them simple advice on achieving a healthy weight in a way that doesn't make them feel patronised.

Links To The Headlines

Third of overweight teenagers think they are right size, study shows. The Guardian, July 9 2015

Generation 'fat-blind': More than a third of obese teenagers think their weight is 'about right', study warns. Daily Mail, July 9 2015

Overweight teens 'do not see themselves as too heavy'. BBC News, July 9 2015

Links To Science

Jackson SE, et al. Weight perceptions in a population sample of English adolescents: cause for celebration or concern? International Journal of Obesity. Published July 9 2015