Tuesday February 4 2014
Sugar should only make up a small part of a balanced diet
“Three fizzy drinks per day could triple chance of heart disease,” says The Daily Telegraph.
Its headline is based on a major US study showing a link between high levels of sugar consumption and a higher relative risk of dying from cardiovascular disease (CVD).
In the study, people who got more than a quarter of their calories from added sugar were almost three times (2.75 to be exact) more likely to die of a CVD than those consuming less than a quarter of their total energy intake from added sugar. It’s recommended that you should not derive more than 10% of your total daily calorie intake from sugar.
The study is relatively reliable because it recruited a large number of people and followed them over more than a decade. However, it was reliant on only one or two daily dietary assessments which may not give an accurate account of a person’s diet and sugar intake over time.
This study indicates that consuming high levels of sugar may be associated with a higher risk of dying from CVDs. It is already known that a poor diet, such as one particularly high in sugar, is linked to a host of diseases, including CVD and cancer. This study does not change the advice to eat a wide and varied diet as part of an active lifestyle in order to reduce the risk of developing many diseases.
Where did the story come from?
The study was carried out by researchers from Centers for Disease Control and Prevention, Atlanta (US) and Harvard School of Public Health. No specific funding source was stated.
The study was published in the peer-reviewed medical journal JAMA Internal Medicine.
Generally the media reported the story accurately. However, reports that there was a tripling of CVD risk from drinking three fizzy drinks per day did not appear to be accurate. The tripling figure appears to relate to a 2.75 increase in relative risk of CVD in those consuming the largest amounts of total added sugar compared to the least. But this was total added sugar and was not limited to fizzy drinks, which was just one aspect of the total added sugar measured.
Sugary drinks are a major source of sugar and should be consumed in moderation. However, there are less obvious sources of sugar, such as processed foods, including tomato sauce, coleslaw and bread.
What kind of research was this?
The research used information from a large US cohort study to prospectively investigate the proposed link between added sugar and death from cardiovascular disease (CVD).
Previous observational studies – the study authors wrote – have suggested that higher intake of added sugar is associated with CVD risk factors. However, few prospective studies have examined this association.
CVD is one of the leading causes of death in England and involves disease of the heart or blood vessels such as coronary heart disease, peripheral vascular disease and stroke.
Added sugar is refined sugar added to food when it is made and processed rather than sugar that occurs naturally in the food, such as the sugars contained in fruit and vegetables. Sugar may be added to improve the food’s flavour and it is often added in high amounts to low fat products, such as low fat yogurts, to replace the flavour lost by removing fat. A practice that seems somewhat self-defeating if people are trying to lose weight.
It is also used in large amounts to sweeten soft drinks. It’s estimated that a standard can of cola contains around 35 grams of sugar which equates to 140 calories.
What did the research involve?
The study obtained information on added sugar intake from a dietary survey of 31,147 nationally representative US adults. The information was then linked to information about deaths and disease in the same people many years later. The researchers were looking for links between the amount of added sugar people were consuming and their levels of death and disease years down the line; specifically deaths from CVD.
The survey research cohort came from the National Health and Nutrition Examination Survey (NHANES) and was linked to death and disease information from the same group (called the NHANES III Linked Mortality cohort). This group was a nationally representative sample of US adults.
Not all of the group (cohort) completing the original survey (n=31,147) had linked death and disease information decades later, many had information missing or were lost to follow up, resulting in a final group of 11,733 that contributed to the study results on death and disease.
The average follow up time for the group between dietary survey and information on death and disease was 14.6 years.
The researchers were mainly interested in the link between added sugar and death from CVD. They adjusted their main analysis for known confounders (factors that could also affect CVD risk) such as age, gender and ethnicity. They also made further adjustments for sociodemographic, behavioural, and clinical characteristics to see if this altered the results.
What were the basic results?
The main results were as follows:
- Most adults in the group (71.4%) consumed 10% or more of their daily calories (energy intake) from added sugar – this is above the UK’s (but not the US’s) recommended limits.
- Approximately 10% of adults consumed 25% or more of their daily calories from added sugar – which is above the US’s recommended limits.
- During a median follow-up period of 14.6 years the researchers recorded 831 CVD deaths.
- Splitting the amount of excess sugar consumed into five equal categories found that the more added sugar people consumed, the higher their risk of death from CVD. The increases in risk, relative to the lowest of the five categories, rose as follows: 7% increase, 18% increase, 38% increase, and finally a 103% increase in risk comparing the top fifth of sugar consuming adults with the lowest fifth.
- Adults consuming 25% or more of their total daily calories from added sugar were 2.75 times more likely to die from CVD than people consuming between 10% and 24.9% of their total calories from added sugars. This is almost three times the risk, which is what was widely quoted in the media reports.
- Despite being in the headlines, the sugar sweetened fizzy drink link with CVD did not feature heavily in the results. They are mentioned only once and were otherwise buried in supplementary data. These data found people consuming seven or more sugar sweetened drinks per week (around one a day) were 29% more at risk of dying from CVD than those who consumed one drink or less a week. Sugar sweetened drinks included fizzy drinks but also energy and sports drinks.
- Only relative risks were reported. No actual risks were stated.
How did the researchers interpret the results?
The researchers concluded that “most US adults consume more added sugar than is recommended for a healthy diet. We observed a significant relationship between added sugar consumption and increased risk for CVD mortality.”
This study used dietary information from a large group of US adults to show that greater added sugar intake was linked to a higher risk of death from CVD.
The study has many strengths including recruiting a large number of people and obtaining information spanning a relatively long time – average 15 years.
The cohort in question was representative of US adults. Despite some ethnicity differences between the US and UK population that may influence the results, the main link between sugar and CVD death is likely to apply to UK adults.
It wasn’t possible to estimate the absolute risk differences of dying from CVD for the different levels of sugar consumption from the results published in the study. This would have been useful to help us better understand the magnitude of the risks involved. All we have is relative risks.
One of the limitations of the study was that it focussed on CVD deaths. The potential links between sugar and risks of other disease, such as cancer, were not assessed.
It was also limited by the method for calculating the dietary intake. This was assessed over one or two 24-hour periods only, with statistical methods used to calculate an estimate of the usual intake. This is not only reliant on accurate recall and reporting of dietary intake at the time, but might not be representative of a person’s dietary intake over 15 years. In their discussion, the authors mention that “major sources of added sugar in American adults’ diet included sugar-sweetened beverages (37.1%), grain-based desserts (13.7%), fruit drinks (8.9%), dairy desserts (6.1%), and candy [aka sweets] (5.8%).”
This study indicates that high sugar levels are associated with a higher risk of CVD deaths.
This research does not change current dietary recommendations to eat a low-fat, high-fibre diet that includes plenty of fresh fruit, vegetables (at least five portions a day) and whole grains. It is also recommended not to obtain more than 10% of your daily calorie intake (energy intake) from sugar. Based on the health effects, sugary foods and drinks should be an occasional treat rather than a daily habit.
Analysis by Bazian. Edited by NHS Choices.
Follow Behind the Headlines on twitter.
Join the Healthy Evidence forum.