These two classic symptoms are directly linked. When blood glucose rises above a certain level, the kidneys cannot reabsorb it all, so sugar spills into the urine. Sugar draws water with it, increasing the volume and frequency of urination, including waking at night to pass urine.
Losing this extra fluid leaves you dehydrated, which triggers strong thirst as your body tries to replace what it is losing. Drinking more then leads to yet more urination, creating a noticeable cycle that often prompts people to seek help.
These symptoms can appear in undiagnosed diabetes or when existing diabetes is poorly controlled. They can also have other causes. If you are experiencing persistent excessive thirst and frequent urination, see a doctor for a blood sugar test rather than assuming the cause, especially if accompanied by tiredness, weight loss, or blurred vision.