Anorexia and bulimia are diseases that can sneak up on someone slowly, but once they have their teeth in you, they are hard to shake. About 20 million girls and women and 10 million boys and men in the United States will be diagnosed at some point with an eating disorder, and 4 to 5 percent of them will die from it.

For those who survive, the journey to recovery is a long one. But the good news is a study by the Eating Disorders Clinical and Research Program at Massachusetts General Hospital of women with these conditions found that up to two-thirds of them recovered over time.

The researchers followed more than 200 women with anorexia and bulimia, all treated at the hospital, over the course of 25 years. They found that 68 percent of the patients with bulimia and 63 percent of those with anorexia had recovered. Recovery was defined as living a year without symptoms.

Bulimia patients got better faster than anorexia patients, but they were more likely to relapse. The study found that more than two-thirds of bulimia patients had recovered by nine years. If they didn’t beat the disease by 10 years, it’s unlikely they ever would, the researchers concluded.

Early treatment is key. Both anorexia and bulimia involve feeling intense guilt and shame around food and weight gain, and depression is common in both. Hospitalization may be necessary for those with serious health problems or low body weight. Antidepressants can help, as well as cognitive, behavioral and nutritional therapy.

If you think someone you know may be struggling, make your concerns known — and take heart that recovery is possible.