How harmful is Sugar?

Sugar is such a health risk that it should be taxed, like alcohol or tobacco. That’s according to a commentary by Dr Robert H Lustig and his colleagues in the prestigious science journal NatureSo how harmful is sugar really? And what do we mean by ‘sugar’ anyway?

We’re not talking here just about the sugar we might add to our tea or coffee. These days most soft drinks, fruit drinks and energy drinks contain added calorific sweeteners, such as sucrose, high fructose corn syrup or fruit juice concentrate. Fructose in particular is an ingredient in many processed foods, including biscuits, ice cream, cereal bars, yoghurt drinks, cakes, pastries, bread rolls and cereals. For example a low fat fruit flavoured yoghurt can contain up to ten tea spoons of fructose based sweetener in one pot.

So we may be consuming a lot more sugar than we realise – which makes it important to know how harmful sugar really is. Is it, as American Professor Richard Johnson claims, ‘an environmental toxin with major health implications.’

Research in recent years has linked sugar with a range of serious health risks and illnesses. These include:

Diabetes – For example a study published in The Journal of the American Medical Association in 2004 suggested sugar was associated with weight gain and an increased risk of type 2 Diabetes in women, whilst a 2010 article in Physiological Behaviour commented, ‘Only recently have large scale epidemiological studies been able to quantify the relationship between SSB (sugar sweetened beverage) consumption and long term weight gain, type 2 diabetes and cardiovascular risk.’  

Non Alcoholic Fatty Liver Disease – A 2008 article in the Journal of Hepatology noted, ‘The pathogenic mechanism underlying the development of NAFID may be associated with excessive dietary fructose consumption.’ A 2009 article in the same journal commented, ‘NAFID patients display higher soft drink consumption independent of metabolic syndrome analysis.’

Hypertension – Research at Imperial College, London, published in Hypertension  found that people’s blood pressure rose significantly for every extra sweetened drink they consumed and suggested the sweetened drinks may reduce nitric oxide in the blood stream, which is essential for keeping healthy blood vessels dilated.

Metabolic Syndrome – ‘In middle aged adults, soft drink consumption is associated with a higher prevalence and incidence of multiple metabolic risk factors.’ That’s according to a 2007 study published in Circulation.

Elevated Blood Pressure – A report in The Journal of the American Society of Nephrology reported, ‘Results suggest that high fructose intake, in the form of added sugar, independently associates with higher BP levels among US adults without a history of hypertension.’ 

Weight Gain and Obesity – As early as 2004 the American Journal of Clinical Nutrition carried an article which commented, ‘Consumption of high fructose corn syrup in beverages may play a role in the epidemic of obesity.’ And a Harvard School of Public Health systematic reviewhasadvised, ‘The weight of epidemiological and experimental evidence indicates that a greater consumption of SSBs is associated with weight gain and obesity. Although more research is needed, sufficient evidence exists for public health strategies to discourage consumption of sugary drinks as part of a healthy lifestyle.’

Cardiovascular Disease – ‘There is also considerable evidence that fructose, rather than glucose, is the more damaging sugar component in terms of cardiovascular risk,’ according to an article in the International Journal of Obesity (London) in 2008.

Cancer – Here the research findings are more mixed, suggesting some groups at risk rather than others. For example an article in the Journal of the National Cancer Institute in 2002 found no statistically significant correlation between dietary glycemic load and pancreatic cancer risk in general. However, it did find a correlation among people who were overweight and sedentary. A 2005 study found no increase of colorectal cancer among women as a result of high intakes of GL, fructose and sugar – but did find an elevated risk among men. More recently a 2011 study advised, ‘Recent observations indicate that cancer cells readily utilize fructose to support proliferation.’

Dementia – A 2010 article in the European Journal of Internal Medicine highlighted, ‘how an excess of dietary carbohydrates, particularly fructose, alongside a relative deficiency in dietary fats and cholesterol may lead to the development of Alzheimer’s Disease.’

There seems to be a growing body of evidence emerging against sugar. However, some commentators view this as too simplistic. Here are some of their reasons:

Evidence from research in one country may not apply equally to another. As NHS Choices points out, for instance, ‘people in the UK consume a relatively low amount of sugar compared with the US and many other countries.’

It is probably simplistic to blame sugar and sugar alone for a range of diseases which are more complicated than that. As NHS Choices points out, other dietary factors may be at work, such as fat and salt – and, as we have reported elsewhere on Age Watch, lack of exercise may also be implicated.

Fructose is associated with a range of serious medical conditions but clinical trials have yet to prove beyond all doubt that it causes them - a point made by the Senior Editor of Harvard Health in 2011.

Some specific associations, in particular with obesity, have been questioned. For example an article in the American Journal of Lifestyle Medicine in 2010 commented, ‘Human studies have shown no unique link between high fructose corn syrup and obesity. In composition, high fructose corn syrup, sucrose, honey, invert sugar and concentrated fruit juices are essentially interchangeable and human studies to date have shown no significant differences in metabolic, endocrine, hormonal or appetite response to these calorific sweeteners.’ This is corroborated by a 2012 systematic review and meta analysis in the Annals of Internal Medicine which advised, ‘Fructose does not seem to cause weight gain when it is substituted for other carbohydrates in diets providing similar calories. Free fructose at high doses that provided excess calories modestly increased body weight, an effect that may be due to the extra calories rather than the fructose.’

Fructose is the main sugar in fruit and fruit is normally perceived as providing health benefits. David Katz, Director of the Yale Prevention Center comments, ‘While fructose as an ingredient excessively engineered into processed foods is, indeed, a problem – I find it far fetched to suggest the native composition of, say, berries, is evil.’ This is a reasonable point, although, as Dr Hitari advises, ‘In nature, fructose found in fruit is provided with excess amounts of fibre, which reduces the rate of intestinal absorption of the sugar’ – a point corroborated by the British Dietetic Association.  

However, this ‘defence’ of sugar is usually relative rather than absolute – typically seeing it as simplistic to ascribe all blame to sugar rather than arguing there is no health risk. Most of the sources we have just noted balance their apparent defence of sugar by noting its dangers. For instance:

NHS Choices notes it is, ‘generally accepted that excessive sugar consumption is bad for our health.’

The Senior Editor of Harvard Health goes on to say, ‘only liver cells break down fructose.. one of the end products is triglyceride, a form of fat. Uric acid and free radicals are also formed. None of this is good. Triglycerides can build up in liver cells and damage liver function.’ He concludes, ‘Every year I attend scores of talks on health and nutrition. Few prompt me to change what I do or what I eat. Lustig’s talk has me looking at the amount of sugar I take in, and thinking hard about sugar in my children’s diets.’

David Katz of the Yale Prevention Center, recognises, ‘An excess of sugar – fructose or any other – is harmful’ and to the extent that he is questioning the critics of sugar it is from a holistic standpoint. As he goes on to say, ‘It is the overall quality, and quantity, of our diet that matters to health – not just one villainous or virtuous nutrient de jour. We should indeed eat food, not too much, mostly plants. The work we need most urgently is about what it will take to get there.’


  • High levels of sugar consumption are associated with a range of serious health risks.
  • We may not realise how much sugar we are consuming because much of it is ‘hidden’ in processed foods and soft drinks.
  • Sugar may be only one of a number of risk factors – with salt, fat and lack of exercise other examples.
  • However, it is likely to be safer to limit our sugar intake.
  • We can do this, for example, by choosing water rather than soft drinks, limiting how much sweet food we eat (like biscuits, cakes and pastries) and checking the levels of sugar in apparently ‘healthy’ foods like cereals, low fat yoghurt and energy drinks. 

Published 01/04/2011, Review date August 2014