Family history of diabetes increases the risk of prediabetes by 26 percent, with effect most evident in non-obese

Prediabetes is a condition most often described as the 'state between normal blood sugar control and full diabetes', and indeed prediabetes progresses to full blown diabetes in up to 20% of individuals affected per year.

Prediabetes can take two forms: impaired fasting glycaemia (IFG), whereby levels of glucose in the fast state are higher than normal but not high enough to be classed as diabetes; and also impaired glucose tolerance (IGT), where blood sugar levels are abnormal due to increased insulin resistance. While it is known that a family history of type 2 diabetes increases the risk of full blown diabetes, research has not yet explored whether such a family history increases the risk of prediabetes in either form.

In this study Fritsche and colleagues analysed 8,106 non-diabetic individuals of European origin collected from the study centres of the German Center for Diabetes Research. Of these, 5,482 had normal glucose tolerance, and 2,624 had IFG and/or IGT n=2,624. They analysed whether having at least one first degree relative with diabetes is associated with prediabetes.

A family history of diabetes was found to increase the crude, unadjusted risk for prediabetes (IFG and/or IGT) by 40%. This increased risk fell to 26% when the analysis took account of age, sex, and BMI of participants.

When different types of prediabetes were considered, family history increased the risk of isolated IFG by 37%, of isolated IGT by 25%, and the two combined by 64%. However overall, when adjusted for BMI, the association between family history and prediabetes was seen only in non-obese individuals (BMI<30 kg/m²). The authors say: "Our data suggest that a family history of diabetes is associated with prediabetes in non-obese rather than in obese individuals. This might indicate the effect of family history on prediabetes becomes readily measurable only when not overshadowed by strong risk factors such as obesity."

They conclude: "We found that family history is an important risk factor for prediabetes, especially for combined IGT and IFG. Its relevance seems to be more evident in the non-obese."