Here’s your Thanksgiving checklist: Eat turkey. Watch football. Talk to your relatives about their health.

Five years ago, the U.S. Surgeon General declared Thanksgiving as National Family Health History Day. Since people tend to be with their loved ones on that holiday, the Surgeon General and the Centers for Disease Control and Prevention are encouraging everyone to use that opportunity to compile a family history.

"Many important diseases, such as diabetes, heart disease, and cancer, run in families," said Rodolfo Valdez, epidemiologist with the CDC’s National Office of Public Health Genomics. "It’s important to know the age at which a person was diagnosed. Diseases that have a strong genetic component tend to show up early in life."

Knowing you are at risk for a disease doesn’t necessarily mean you can avoid getting it. But instead of developing the illness at age 40, you may be able to postpone its onset until age 60.

"We know that diabetes runs in families," said Maureen Stoy, certified diabetes educator at Northeast Georgia Medical Center. "With each generation, people seem to be developing diabetes earlier, mainly because of poor diet and obesity. People who know they have a history should get tested sooner, so they can make lifestyle changes and prevent complications."

Dr. Marti Gibbs, a family practice physician with the Longstreet Clinic in Oakwood, said she always reviews family history when she sees a new patient for the first time.

"It’s incredibly helpful," she said. "It guides us on what we need to know in terms of prevention."

There are specific guidelines on when patients should be screened for certain diseases. For example, a woman’s first mammogram is recommended at age 40, and she should be tested for colon cancer beginning at age 50.

But when a patient is at high risk for an illness, doctors may diverge from the standard schedule.

"We try to be very proactive," said Gibbs. "If you have a family history of heart disease, I may get an EKG a lot earlier. If you have a mom who developed breast cancer at age 35, I will order (your first) mammogram 10 years earlier than I normally do."

Obviously, people who were adopted are at a disadvantage, because they may not know the medical history of their biological parents. But Valdez said a family history can still be useful even for people who were not raised by blood relatives.

"Traditional risk factors such as smoking and obesity are usually much more powerful than genetics," he said. "If your (adoptive) parents were heavy smokers, you may have been exposed to secondhand smoke. If they had bad diets, you’re more likely to be obese."

On the other hand, there are many genetic diseases that will occur regardless of the person’s environment. Autoimmune disorders such as lupus, rheumatoid arthritis, and multiple sclerosis fall into this category. If someone carries the gene, they can develop the condition despite a healthy lifestyle.

But Gibbs said it’s still useful to know whether there’s a family history. "Even if you can’t prevent the disease, at least you’ll know what symptoms to look for," she said.

That’s true not just for yourself, but for any children you might have, now and in the future.

"Knowing which diseases run in your family can be helpful to couples who are thinking about having children," said Kimberly Redding, senior director of the Office of Healthy Behaviors at the Georgia Division of Public Health.

She said people who have a family member with a condition such as sickle-cell anemia or cystic fibrosis should receive genetic testing and counseling so they will know what to expect.

Knowledge about a family’s disease risk isn’t always passed down from older generations to younger; sometimes it works in reverse.

Clermont resident Natalie Ledford, now 13, was diagnosed several years ago with long QT syndrome, a potentially fatal heart rhythm disorder.

The condition often isn’t detected through standard heart tests such as EKGs. People who have long QT may have a tendency to faint without warning. They also may have had relatives who suddenly dropped dead for no apparent reason.

"Nobody knew what Natalie had," said her grandmother, Doris Ledford. "If we had known that this runs in our family, they could have diagnosed Natalie sooner. Once we found out, we had to kind of work backward and figure out who else had it."

A genetic test showed Natalie had the type of long QT that’s caused by a mutated gene. After her diagnosis, the rest of her family underwent genetic testing. It turned out that Natalie’s father and grandfather also carried the trait.

Doris Ledford said the discovery solved a long-standing family mystery. "Her grandfather, my husband, had a heart attack at age 36. No one knew why," she said.

She said Natalie’s father has not had symptoms so far. But both men are now on medication to keep their hearts regulated.

Ledford said she’s glad to see that families are being encouraged to record their health history. "I think it’s a wonderful idea," she said.

Government health agencies are trying to make record-keeping as easy as possible. Both the CDC and the Surgeon General offer links on their Web sites to an online tool, "My Family Health Portrait."

The program asks users to provide as much information as they can about the health of their first-line relatives: parents, siblings, grandparents and children.

For each family member, you list their major illnesses and what age they were at the time of diagnosis. When you’re finished, the program will create both a written record and a "family tree" diagram that allows you to track any disease through color-coding.

"You should share this information with your health care provider," said Redding.

According to the CDC, thee are some "red flags" you should watch out for in your family history, including:

diseases that occur at an earlier age than usual; more than one close relative with the same disease; and a disease that normally doesn’t affect a certain gender (such as breast cancer in a man).

You should also look for certain combinations of diseases in your family. For example, if you have breast cancer and your sister has ovarian cancer, you may want to be tested for BRCA, a genetic mutation that can cause both of those diseases.

Editor's note: The CDC Web address in this story was updated in January 2010.