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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Sugar's Role in Diabetes

October 10, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Diabetes mellitus is a common disorder marked by the elevation of blood sugar. Diabetes develops most commonly because the pancreas is injured and is unable to produce enough insulin (type 1 diabetes) or because the body's tissues become resistant to insulin, requiring more of it than the pancreas can produce to keep the blood sugar normal (type 2 diabetes). The biggest risk factor for insulin resistance is obesity.

Although the majority of patients with type 1 diabetes develop this disease in childhood or early adulthood and the majority of patients with type 2 diabetes are well into adulthood when they develop the disease, the terms juvenile-onset diabetes (for type 1) and adult-onset diabetes (for type 2) have fallen out of favor. Either type may occur at any age. In fact, because obesity among children is increasing, type 2 diabetes rates are soaring in children. In addition, the terms insulin-dependent and non-insulin-dependent have also been retired. Although insulin therapy is a typical approach to type 1 diabetes, either type of disease may (or may not) require insulin therapy.

The most common complications of diabetes include eye damage, nerve disease and problems with kidney function, although other problems including heart attacks, stroke, joint and tendon disease and infections may occur with increased frequency. Medical treatment can often delay the development of complications or prevent them altogether. Given how common diabetes is and how many problems can develop as a result, a clearer understanding of the cause could lead to effective means of prevention.

The Cause of Diabetes

The cause of diabetes in any individual is usually unknown, although there are a host of theories. Ongoing research is attempting to get a better understanding of how this disease develops. Well-recognized risk factors include:

  • Heredity
  • Obesity
  • Medications
  • Viral infection (probably rare)

In recent years, regular consumption of foods with a high "glycemic index" — a measure of how quickly blood sugar rises when you eat particular foods — has been identified as a possible risk factor for a person developing diabetes. However, plenty of people eat these foods and never develop the disease. In addition, foods with high glycemic index may have similar sugar content as foods with a low index. This remains an area of active investigation, including the possibility that maintaining a diet with a low glycemic index may reduce the risk of diabetes, especially among people with a family history of the disease.

Sugar and Diabetes: Dispelling the Myth

A person with diabetes is generally advised to avoid foods with a high sugar content and to maintain a diet and medication schedule that maintains as normal a blood sugar level as possible. Improved blood sugar control may reduce the chances that certain complications of the disease will develop. But just because the disease is characterized by an elevated blood sugar level and because lowering the blood sugar level is an important goal of therapy, a high-sugar diet does not cause the illness. An elevated blood sugar level is a result of having diabetes, not the cause.

Assuming an elevated blood sugar level is the cause of diabetes is like assuming that coughing is the cause of pneumonia. And not only does sugar itself not cause diabetes, there is no convincing evidence that sugar causes other problems that it has been blamed for, such as hyperactivity. Many medical myths develop along these lines.

Dispelling this myth regarding sugar may correct the assumption many people have about the development of diabetes — that people with this illness have brought it on themselves by eating the wrong kinds of foods. Although it is true that avoiding obesity may reduce the chances of developing type 2 diabetes, the specific types of foods you eat may play little or no known role. And not all persons with diabetes are overweight — that's another myth. For these patients, heredity and perhaps other undiscovered factors are more important.

The Bottom Line

In recent years, researchers have found that exercise, a healthy diet, losing excess weight and medication for mild elevations in blood sugar (sometimes called "pre-diabetes") may delay the onset of type 2 diabetes. Unfortunately, limiting sugar intake is not a reliable way to prevent diabetes -- unless it helps avoid excess weight. Research is underway to identify genetic, immune, dietary or other environmental factors that contribute to disease development in the hopes of preventing disease, especially in persons at high risk. But, for now, the notion that a high-sugar diet causes diabetes is a medical myth that demonstrates how the effect of an illness may be mistaken for its cause.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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