How do I know whether my blood sugar is healthy (prediabetes)?

You check your blood sugar through a blood test at your GP's practice, not at home. There are three types of test. A fasting measurement of 100–125 mg/dL indicates prediabetes. In an oral glucose tolerance test, where you drink a sugar solution and are measured two hours later, 140–199 mg/dL falls in the prediabetes range. The HbA1c test shows your average blood sugar over three months; 5.7%–6.4% falls in that same range.

Prediabetes is not a foregone conclusion. Each year, around 10% of people with prediabetes do go on to develop type 2 diabetes, but about one third return to normal levels on their own. The majority, two thirds, do not develop diabetes even after several years. Typical diabetes complications such as eye or kidney damage do not occur with prediabetes itself. Reason for attention, then, but not for panic.

There is, however, a slightly elevated risk of cardiovascular disease. That is probably due more to accompanying factors such as excess weight and high blood pressure than to the mildly raised blood sugar itself. The absolute risk is small: fewer than 9 extra cases per 10,000 people per year¹.

The most powerful approach is intensive lifestyle change: fewer calories, at least 150 minutes of exercise per week, and personal coaching. This prevents the progression to diabetes twice as effectively as the medication metformin, roughly 6 fewer cases per 100 people per year compared with 3 for metformin². The combination of endurance training, such as brisk walking or cycling, and strength training produced the best overall results for blood sugar, weight and cholesterol in research. Endurance training more often led to a return to normal values (69% versus 43%), while strength training improved insulin sensitivity more strongly. This comes from a small study of 70 people, so it is preliminary³.

A small study of 15 participants found that eating vegetables and protein first and carbohydrates last reduced the post-meal blood sugar spike by more than 40%. The evidence base is still too narrow for firm recommendations⁴. Metformin can reduce the risk of diabetes, but is less effective than lifestyle modification. Because two thirds of people with prediabetes never develop diabetes, medication is not necessary for everyone. It appears most worthwhile for women with a prior history of gestational diabetes, people under 60 with a BMI above 35, or people with a fasting glucose above 110 mg/dL or an HbA1c above 6.0%⁵.