It's hard enough being a kid. When you have a disease that's supposedly for old people, it's that much more difficult.

Sadly, more kids are being diagnosed with problems that were once thought of as adult diseases. Some of these conditions, such as Type 2 diabetes and overuse injuries, are unfortunate consequences of modern life, as both obesity and intense athletic training have become common among children.

Others, such as multiple sclerosis are being diagnosed in kids as researchers better understand the disease in adults.

"Certainly, environmental factors affect things," said Dr. Evan Hadley, associate director of the gerontology research program at the National Institute on Aging.

"Now people are reporting conditions that they hadn't reported before," Hadley said, so the upswing in diagnoses of adult diseases in kids "is a plausible thing."

DIABETES

Taniuska Nunez inhabits two realities. At 12, she wants nothing more than to live in the moment and enjoy her favorite foods and drinks. It is a constant struggle to grasp the idea that they could kill her.

Two years ago, the Bronx seventh-grader learned she had Type 2 diabetes. As many as half of new diabetes diagnoses in American children are Type 2, once called "adult-onset" diabetes, according to the Centers for Disease Control. The agency projects that children born in 2000 have a 1 in 3 risk of developing diabetes; for Hispanic kids like Nunez, the risk is 1 in 2.

Doctors agree that the trend is linked to overweight. The increased demand for the blood sugar-regulating hormone insulin rises as kids eat more, but in those with a certain genetic predisposition, the body cannot meet that requirement.

Because there is no cure for the disease, patients must regulate their blood sugar by watching their diet, exercising and, in some cases, taking glucose-regulating medications.

But sticking to those changes over the long term is tiresome. Like 43% of New York City's elementary schoolchildren, Nunez is overweight. She panicked and cried when her doctors told her she'd have to stop drinking soda and eating chips and cookies.

"I felt like, 'I don't care if I have diabetes; I'm still going to eat it,'" Nunez recalled during a recent visit to the South Bronx Health Center for Children and Families, where 65% of overweight kids show signs of insulin resistance, according to pediatrician Dr. Marian Larkin. "Then I found out what could happen, that I could die because of it."

What's the best way?

At the Naomi Berrie Diabetes Center at Columbia University Medical Center, Dr. Robin Goland is testing strategies to help children manage their disease; they may develop complications such as heart and kidney disease faster than people who are diagnosed in adulthood. In her trial, kids are randomized to one of two groups: those who receive medication alone, and those who take glucose-regulating drugs with the help of a coach who teaches them lifestyle changes, including exercise. Physical activity is thought to encourage the metabolism of the carbohydrates that drive the body's demand for insulin.

"This is not a group that wears seatbelts; they're invincible," said Goland, the center's co-director. "They're teenagers and this is a disease associated with a much older age group that has no symptoms. To ask teens to do something when they feel fine is asking a lot - it's a lot for adults."

Nunez carries her glucose-regulating pills around with her, but sometimes she forgets to take them, she said.

Meanwhile, her mother frets that 7-year-old brother Kevin shows signs of Type 2 diabetes, too.

"Every day, you have to check yourself on your finger to see if your sugar is all right," Nunez said. "Sometimes you forget. You go to public places and they're looking at you because of it."

When that happens, she said, "I feel a little sad."

OVERUSE INJURIES

A soccer player since the age of 4, Shana Chock-Goldman was not totally surprised when she tore her anterior cruciate ligament, which connects the thigh to the shin. Girl soccer and basketball players are three to five times more likely than boys to suffer the injury because their bones may be weaker, said Dr. Eric Small, director of Family Sports Medicine & Fitness of New York in Mount Kisco.

But Chock-Goldman, of Irvington, was incredulous when she tore her ACL a third time at 17, four years after the first injury and two years after her second.

"The third time, I tried to deny it," she said. "I was like, 'This is not happening to me.'"

A heavy emphasis on year-round sports training and competitions has resulted in a surge of overuse injuries in children. About 15 million kids from sixth to 12th grade participate in organized sports, and half of them are thought to suffer some type of overuse injury, Small said. Of those, 1%-10% are seriously injured.

"In the past four years, we've seen a 50% jump in these adult types of injuries," said Vinny Sullivan, director of FormÈ Health and Fitness in Scarsdale. "They could practice anywhere up to six hours a day, and five or six competitions a weekend. Professional athletes don't do that."

These kids are overworking certain bones and muscle groups as they attempt to master one sport, rather than conditioning their whole body by playing a variety of sports. In addition, kids' bones are weaker as they grow. Too much running and jumping can lead to a shin or an ankle stress fracture. Too much throwing of a baseball or serving a tennis ball can result in a shoulder or an elbow stress fracture.

Consequently, children can be left with chronic pain and the risk of osteoarthritis 10-15 years after their injury - long before a person typically develops arthritis, Small said.

In the case of teens like Chock-Goldman, they also may face early retirement from their favorite sport. The Connecticut College freshman joined her school's crew team when her last injury made it impossible to continue playing competitive soccer.

"My life was soccer, so it was very hard to give that up," she said. "Now I'm doing crew and it's great because it doesn't hurt my knees at all.

"A lot of the girls are former athletes that injured themselves," Chock-Goldman added. "There are a couple girls on my team with ACL surgeries in their past."

MULTIPLE SCLEROSIS

One morning two years ago, 10-year-old Lee Goncalves woke up seeing double. "Wash your face," his mother told him, but rinsing the sleep out of his eyes didn't improve his vision.

Within days, doctors had scanned Lee's brain and drawn fluid out of his spinal cord. The diagnosis, multiple sclerosis, was as foreign as it was unreal. MS usually strikes adults between 20 and 50, attacking the central nervous system and causing symptoms including numbness, spasticity, pain and cognitive problems, among other things.

"I couldn't believe what they were telling me," cried Lee's mother, Sonia Goncalves, of Bay Shore, L.I. "Why my son? Why'd my son have to be the kid with an adult disease?"

An estimated 15,000 children in the United States have multiple sclerosis, according to the National MS Society. But until 10 years ago, when drugs that slow the disease became available, "children hadn't been diagnosed with MS," said Deborah Hertz, the society's national director of medical programs. "It was very rare."

At the National Pediatric MS Center at Stony Brook University, doctors are documenting what MS looks like in the kids they see, 53% of whom are African-American or Hispanic. They are also trying to tease out what environmental factors may trigger the disease.

"The degree to which kids differ from adults is still an open question," said Dr. Lauren Krupp, the center's director.

may help shed light Still, children with MS may ultimately better help doctors tease out what environmental factors trigger the disease in people who may have a genetic predisposition toward it.

"With the 47-year-old, you're going to have to go through 47 years of environmental exposure," Krupp said. "In a 7-year-old, if nothing else, you only have to go through seven years of exposure."

For the patients themselves, though, the disease is defined by what happens outside the research lab.

On Tuesdays, Thursdays and Sundays, Lee's mother and sister give him a shot in his arm, stomach or hip. Sometimes he asks Goncalves if he really has to take it, but he never refuses, she said.

Instead, her son watches TV to distract himself.

"It hurts a good 5 seconds and then it goes away," Lee, now 13, said.

Most difficult for Lee is telling Goncalves when he's not feeling well, a sense of protectiveness that's common among MS-stricken children who want to shield their parents from additional worry, said Maria Malazzo, a social worker in the Stony Brook program.

"I have to tell her, but it's hard," Lee said. "My mom, she'll start crying. I tell her it's going to be okay."

On the horizon

As American children grow heavier, doctors are studying whether overweight kids are affected by other "adult" diseases besides Type 2 diabetes. A March study in the New England Journal of Medicine reported that life expectancy will decline by as many as five years for this generation of children unless the obesity epidemic is reversed.

Among the most worrisome prospects for these children is cardiovascular disease, the leading cause of death in the United States. Recent studies suggest that a combination of overweight and a sedentary lifestyle already has kids' hearts more closely resembling those of their parents.

One in five teenagers has deterioration of tiny blood vessels usually associated with heart disease in adults, according to research presented at a science festival last year by Dr. Faisal Khan of the University of Dundee in Scotland. Only some of the teens were overweight, and they had no symptoms of heart disease. None was diabetic.

But youngsters with Type 2 diabetes suffer from the same problem, researchers at Children's Hospital of Pittsburgh have found. Children as young as 8 who have Type 2 diabetes or are obese have early signs of arterial stiffness comparable to adults as old as 59. These children are at increased risk for premature aging of the cardiovascular system, according to the hospital's Dr. Silva Arslanian.

"They're setting the stage for high blood pressure," said Dr. Robert Butler, president of the International Longevity Center in Manhattan. "It's not pretty and there's no immediate feeling that we're solving this problem."

Joint pain is another concern for heavy kids. Their weight wreaks havoc on their knees, Butler said. "It's so important that we begin to address children's health habits and address the sedentary impact," he said.

The five fewer years today's children may live because of modern habits is not a trivial number, Butler added.

"That's significant. That's a lot of life, especially in the aggregate," he said. "The toll is enormous."