Research published this month in the Annals of Internal Medicine shows a significant spike in the rates of diabetes in the U.S. over the past two decades. In particular, the prevalence of prediabetes has risen from 5.8 percent between 1988 and 1994 to 12.4 percent between 2005 and 2010.

Dr. Kathleen Figaro, an endocrinologist with Genesis Health System in Bettendorf, Iowa, told Healthline that a shrinking “cost per calorie” ratio in our food is partly to blame for the increase. “There is an excess amount of corn being produced, and it has to go somewhere. It is being used to make high-fructose corn syrup that is added to foods and decreases the price per calorie,” she said.

As a result, we get dense, highly processed foods that are readily available, said Figaro. They can be bought cheaply in inner cities or other so-called “food deserts,” where access to quality, fresh foods is limited.

Tami Ross, a certified diabetes instructor in Lexington, Ky., who served as the president of the American Association of Diabetes Educators, told Healthline that age 40 is the “magic number,” when diabetes begins to sneak up on people. She said that everyone 40 and older should take the interactive type 2 diabetes screening test provided by the American Diabetes Association (ADA).Diabetes occurs when the body does not process sugar properly. Nonwhites, people who are overweight, and those with a family history of diabetes are at a higher risk. Almost 26 million people in the U.S., or 8.3 percent of the population, have diabetes, according to the ADA. Type 2 diabetes tends to affect people as they get older. About seven million people in the U.S. have type 2 diabetes and don’t know it.

Symptoms that many people assume are just a natural part of getting older may actually point to diabetes. Everyone should be checked for diabetes by the age of 45, according to the ADA. A simple blood test is usually all that's needed.

Figaro and Ross helped Healthline compile this list of symptoms that may be signs of diabetes, not just normal aging.

Your vision seems to be in decline. When you switch from looking at something near to something far away and lose focus, it can be a sign of uncontrolled blood sugar. If you got glasses just a year ago but seeing has already become difficult again, take note. “Sometimes my patients say they suddenly found themselves needing stronger reading classes,” Ross said.

You’re too exhausted to do anything. “My patients often say they are wading through molasses,” said Ross. Lack of energy is a common symptom of diabetes. Energy ebbs because the body is not turning sugar into energy in the right way.

There are "dirty" patches on your neck, or you have dark circles under your eyes (“raccoon eyes”). Too much glucose in the bloodstream damages blood vessels and can create these skin conditions, as well as tingling and numbness in the hands and feet. Dry, itchy skin may also develop. There is even a movement afoot among barbers to learn to spot the signs of diabetes on the skin and the scalps of their clients, Ross said.

You’re up all night using the bathroom and can never seem to get enough water. “That unquenchable thirst is a classic symptom [of diabetes],” Ross said. “Your body is trying to flush out the sugar and it doesn’t do a good job. More thirst, more fluids, more going to the bathroom.”

You’re always hungry, on top of being tired and angry. “I need fuel, so you think 'eat, eat, eat,'” Ross explained. “But it’s just floating around your bloodstream. In the end it’s not being used well.”

Many symptoms of diabetes can ultimately make a person grouchy, Ross added.