I don't have a simple answer for you. Type 1 diabetes (the kind that occurs during childhood and used to be called "juvenile diabetes") seems to develop more often in winter than summer, and is more common in areas with cold climates. Among Caucasians, who have a higher risk of type 1 diabetes than any other race, diabetes risk varies geographically, and is generally higher among Northern Europeans than Southern Europeans. While this may suggest that climate is a contributing factor, the experts at Harvard's Joslin Diabetes Center note that the risk is also high in Sardinia, an island in the warm Mediterranean near Italy, a fact that would seem to contradict the notion that cold climate is a risk factor for diabetes.
Weather has no direct effect on diabetes control but can affect it indirectly. While your blood sugar doesn't go up or down in response to hot or cold outdoor temperatures, weather does have an impact on eating and exercise habits, which can in turn influence how well you're able to control your blood sugar. Then there is the fact that bad weather can lead to depression and anxiety, which, in turn, can affect blood-sugar management. In the summer, diabetics are among those most likely to suffer as a result of heat stress and high humidity.
Another consideration: if you're on insulin, you have to be very careful of where you store it during hot or cold weather, it will break down and won't work if it gets exposed to temperature extremes.
Andrew Weil, M.D.