(CNN) -- Yulia Gorelik describes her 8-year-old son, Daniel, as "a very clever boy." He plays "Fur Elise" with elegant ease on the piano and enjoys eating McDonald's chicken nuggets.
Mother and son arrived in the United States this summer through an organization called Hope for Chernobyl's Child. Gorelik had faith that American doctors could fix Daniel's headaches, weakness and vertigo during their six-week stay.
"I have the hope that we can do something here to make him stronger, because he is intelligent, he is nice, but his body is weak," Gorelik, 34, said in July.
The Goreliks live in a region called Gomel, Belarus, which was heavily hit with radioactive fallout from the worst nuclear accident the world has ever seen.
On April 26, 1986, explosions at a reactor at Chernobyl in Ukraine produced radiation effects almost 14 times greater than the 2011 Fukushima Daiichi disaster in Japan and 400 times more powerful than the 1945 atomic bomb dropped on Hiroshima.
More than 2 million people in Belarus were affected by the Chernobyl disaster, according to the World Bank. Two-thirds of the contamination from the accident fell in Belarus, diminishing the quality of life in the region.
Hope for Chernobyl's Child helps 10 to 15 children living in Belarus find host families and dental and medical care in Washington state every summer. The organization also helps families on the ground in Belarus by delivering humanitarian aid.
Medical and dental care are lacking in areas affected by the disaster, Hope for Chernobyl's Child says. Families there often earn little money and have limited job opportunities, making it difficult to provide food, clothing and medications for their children.
Ask Gorelik whether her son's health problems are caused by radiation, and she says, "Yes, of course."
But the reality is much more complex.
What does radiation really cause?
People who lived in the areas that received significant contamination from Chernobyl in 1986 have been the subject of many scientific studies. But researchers haven't looked much at health problems in the region's children who weren't yet born at the time of the disaster, said Scott Davis, epidemiologist at the Fred Hutchinson Cancer Research Center at the University of Washington.
The lack of hard evidence doesn't mean that lingering radiation isn't causing harm in some ways, Davis said, but it would be difficult to establish that anyone's particular disease or condition stems from low-dose radiation exposure over a long period in that area.
"This is a major problem in talking with people who, either themselves or someone close to them, (are) sick," he said. "To say, 'Well, we don't see any risk' -- people just can't get their head around that."
The issue is complicated because cancer, for example, caused by radiation looks exactly like cancer that developed for other reasons, experts say. There's no "Chernobyl" name tag on tumors in people who suffered radiation exposure.
Scientists know radioactive iodine-131 got into the human body when people drank milk from cows that ate contaminated grass, said Dr. Fred Mettler, professor emeritus of the Department of Radiology at the University of New Mexico. This led to higher incidences of thyroid cancer in people who were children at that time -- such as Yulia Gorelik, who underwent treatment at age 12.
More than 4,000 such cases were diagnosed from 1992 to 2002, but it's impossible to say which ones were caused by Chernobyl radiation. Mettler said the iodine is unlikely to have caused cancer in anyone born later -- especially because iodine-131 has a half-life of eight days, so in about two months, it's almost undetectable.
Another radioactive chemical from the reactor explosion, Cesium-137, has a half-life of about 30 years, so it stays around a lot longer than iodine-131 and can still be measured in some soils and foods in several areas of Europe. Still, the dose to which people in the area have been exposed isn't very high, Mettler said.
The doses from cesium contamination "are low and insufficient to cause effects, had there been any," said John Boice, professor of medicine at Vanderbilt University School of Medicine and president nominee of the National Council on Radiation Protection and Measurements.
"A lot of the issues become: Are the health things really due to Chernobyl, or are they things which would have occurred anyhow?" Mettler said.
Zones of uncertainty
For Jennifer Henning, president of Hope for Chernobyl's Child, there's no question that the ailments the children in the program suffer are the result of radiation exposure.
"I've seen the health effects firsthand," Henning said. "I know that it's there."
A physical education teacher in one of the schools that the organization works with told her that children there are getting weaker and weaker, Henning said.
That there are serious health problems among many youths in Belarus is not in dispute.
In 2008, nearly 22% of adolescents in Belarus had chronic diseases and disabilities, according to a 2010 UNICEF report. Risk factors, according to this report, included smoking and using alcohol and drugs.
Experts say that what organizations such as Hope for Chenobyl's Child are doing to help children with medical problems -- providing assistance in Belarus and flying them to the United States for medical respite -- is great. Several other organizations also operate in regions devastated by the Chernobyl accident, such as Chernobyl Children International, the Chernobyl Children's Project and Chernobyl Children's Trust.
But rather than radiation-related illness, according to the 2005 Chernobyl Forum report, "The most pressing health concerns for the affected areas thus lie in poor diet and lifestyle factors such as alcohol and tobacco use, as well as poverty and limited access to health care."
The cause of Chernobyl evokes greater sympathy from the public than some other causes might, Mettler said.
"It's a very unique, scary accident," he said. "Everybody in the world knows about it. But, if you were to say, 'I've got children starving in the Sudan,' people would go, 'huh, whatever.' It wouldn't get their attention."
Henning points to a 2009 report, published by the Annals of the New York Academy of Sciences, rounding up evidence that radiation has had a lasting effect on the health of the population in contaminated areas. In Belarus, for instance, cancer morbidity increased 40% from 1990 to 2000, the report said, and girls age 10 to 14 born to irradiated parents had an increase in malignant and benign neoplasms.
Mettler counters this with the Chernobyl Forum report and a report from the United Nations Scientific Committee on the Effects of Atomic Radiation, which both had stamps of approval from representatives of the governments of Russia, Belarus and the Ukraine.
The Chernobyl Forum report said that while increases in congenital malformations in children have been reported in Belarus since 1986, the rates are not related to radiation and "may be the result of increased registration" -- i.e. more people reporting their family's health problems.
"The majority of the 'contaminated' territories are now safe for settlement and economic activity," although certain restrictions need to remain in place on the use of land in some areas, the report said.
More than 5 million people in Belarus, Russia and Ukraine living in "contaminated" areas received whole-body radiation from the accident, but in doses not much higher than the natural radiation in the environment, the report said.
Does that mean that a healthy person could safely move to an area that has been cordoned off for decades and not have an increased risk of cancer? Davis isn't so sure -- but said he believes it hasn't been studied extensively enough.
"Common sense would dictate that it's probably not a great idea to live in a highly contaminated area and eat produce produced in the fields that are contaminated, or be in constant exposure mode," Davis said.
A mental toll
Both international reports highlighted the mental health toll as well; the Chernobyl Forum report called this the greatest public health problem that the accident caused. More than 330,000 people were relocated from the hardest-hit areas, which was a "deeply traumatic experience" for many.
"There is no question that people who either are exposed to radiation or think they might have been, suddenly are very nervous, and every time something happens, they go, 'Oh, my God, what is this? Do I have a problem?' And they dash off to the hospital," Mettler said.
Studies have shown that this population has a higher level of anxiety and are more likely to report that they have physical symptoms that they cannot explain, according to the Chernobyl Forum report. They're also more likely to say they are in poor health.
The report noted that as the media began to speak of "Chernobyl victims" and governments offered disaster-related benefits, "rather than perceiving themselves as 'survivors,' many of those people have come to think of themselves as helpless, weak and lacking control over their future."
Gorelik was not evacuated after Chernobyl. She grew up in the region of Gomel, the same area where she and Daniel live today. About a 20-minute drive away is the "Dead Zone," where entire villages have been abandoned since 1986.
Getting medical care
Gorelik and Daniel stayed with Henning's family in the Seattle area during part of the summer. They returned to Belarus at the beginning of August, Henning said. During their time in the Pacific Northwest, they saw the ocean, mountains and a rainforest, in addition to various doctors. Daniel put on 4.5 pounds during the six-week stay.
"Yulia and Daniel saw various doctors and it was determined that many of their health issues could be attributed to the poor nutrition that is so common in this area of Belarus," Henning said in an e-mail.
Among the nine children and two adults, including Gorelik, who spent this summer in the United States through Hope for Chernobyl's Child, a total of 47 cavities were filled, four wisdom teeth were pulled, and 60 blood tests were taken, Henning said. The Belarusians gained a combined total of 26.5 pounds.
Gorelik said in July that Hope for Chernobyl's Child has given her not only material help but also mental support. The gratitude she feels toward the organization and her hosts is immeasurable, she says.
Reflecting on her situation, her words about lack of control are reminiscent of the Chernobyl Forum Report: "If you are living in bad conditions, sometimes, you feel like you are alone. You don't have control of your life. You don't have any support. You don't have any hope, maybe. There is only one hope, to God. But if you meet some people who can give you their hands, and their help, it is making you stronger, it is making you happy, really happy. That's why I'm grateful with all my soul."
Gorelik and Daniel left for their long journey back to Belarus on August 5, including a 13-hour layover in Frankfurt. Henning and colleagues arranged for them, and the others in the Hope for Chernobyl's Child group, to rest in a lounge at the airport.
Such cross-cultural friendship has become part of the fallout of Chernobyl.