Without it, they can go blind, lose a limb, or develop life-threatening kidney problems or heart disease.
It's just one thing that weighs heavily on the mind of car dealership president Eric Rehkemper.
He stays cool under pressure, all while managing Type 1 diabetes.
"24/7, seven days a week, whether you're on vacation or whether you're working the job," said Rehkemper.
"It's something that always factors into everything you're doing."
The only approved drug to keep Type 1 diabetics alive is insulin, but it's dangerously easy to over and under-dose.
"Insulin is difficult and risky and challenging," said Dr. Janet McGill, an endocrinologist at Washington University.
The treatments for Type 1 and 2 diabetes are different. But doctors are now trying Type 2 drugs in Type 1 patients.
"What these drugs offer is a little reprieve from doing everything perfectly just with insulin," said Dr. McGill.
One class of Type Two drugs called GLP-1 receptor agonists lower insulin doses and improve blood sugars.
Another class, called SGLT-2 inhibitors significantly lower blood sugar levels for many Type 1s.
"It reduces some of the very high blood sugars that occur after meals," said Dr. McGill.
SGLT-2 inhibitors also improve heart and kidney health.
"Some get quite noticeably good results," she said.
Eric has seen big improvements in his blood sugar by taking an SGL-2 inhibitor along with his insulin.
"It has been such a great improvement on my body," said Rehkemper. "Probably added ten, 15 years to my life, I would say."
Another common drug for Type 2 diabetes, metformin, has also shown to reduce insulin needs for some Type 1 diabetics while improving blood sugar control.
Other drugs are not so certain.
"Sotoclofosin was presented to the FDA after a couple of large clinical trials in Type 1 diabetes," said Dr. McGill. "And the advisory committee's split."
She said the FDA declined to approve sotoclofosin for use in Type 1 diabetes.
"But there are four others actually," she added, "so we don't know the outcome, what the FDA will say about the others."