Causes of Type 1 Diabetes
Type 1 diabetes is caused when the immune system, which normally fights harmful bacteria or viruses, attacks and destroys the insulin-producing cells in the pancreas leaving a person with little or no insulin. Instead of being transported into the cells, sugar builds up in the bloodstream.
Causes of Pre-Diabetes and Type 2 Diabetes
In pre-diabetes, which can lead to type 2 diabetes, and in type 2 diabetes, the cells become resistant to insulin, and the pancreas is unable to make enough insulin to overcome this resistance. Instead of moving into the cells, sugar builds up in the bloodstream. Exactly why this happens is uncertain, although excess fat, especially abdominal fat, and inactivity seem to be important factors.
Causes of Gestational Diabetes
During pregnancy, the placenta produces hormones to sustain pregnancy. These hormones make cells more resistant to insulin. As the placenta grows larger in the second and third trimesters, it secretes more of these hormones, making it even harder for insulin to do its job.
Normally, the pancreas responds by producing enough extra insulin to overcome this resistance. But sometimes the pancreas can't keep up. When this happens, too little glucose gets into the cells and too much stays in the blood.