Japan's reclusive and troubled Crown Princess Masako said Tuesday that her health is improving and she is feeling more able to take part in social activities.

Her father-in-law, Emperor Akihito, is also suffering from stress and inflammation of the stomach, the Imperial Household Agency said Tuesday. Akihito, who turns 75 later this month, had surgery for prostate cancer in 2003.

Masako, who married Crown Prince Naruhito in 1993, has skipped much of her duties in the last five years, mostly because of stress-related symptoms and mental depression.

"My performance still is not at its best, but I'm beginning to feel I'm now able to do more things, little by little," she said in a statement for her 45th birthday on Tuesday.

Royal doctors said Masako has made "steady progress" over the last two years, and is starting to resume public appearances, including welcoming Spanish King Juan Carlos and his wife, Queen Sofia, last month — her first participation in an official event in five years.

But they warned she remains unstable and needs rest.

"The biggest reason for her condition is that she has unpredictable ups and downs in her physical and mental condition," the doctors said in a statement Tuesday.

Though she was reportedly feeling better mentally, the Imperial Household Agency said Masako canceled meetings Tuesday with the Emperor and the Empress, as well as palace officials, because of a fever and sore throat associated with a cold.

Speculation about Masako's health has become a staple of the Japanese media. Some tabloid magazines and newspapers have criticized her for lavish dinners and shopping outings while missing her official duties.

Although Masako has been seen on nationally televised news shows attending family events at her 7-year-old daughter Aiko's school, she has skipped formal events that are standard fare for Japanese royalty, such as greeting guests, attending charities and making overseas trips.

Public expectations for Masako, a former diplomat and Harvard graduate, were high from the moment she became engaged to Naruhito, with many hoping she would be a role model for the modern Japanese woman.

The couple's failure to have a son has put a great deal of pressure on the princess as only sons can inherit the country's Chrysanthemum Throne. Masako had a miscarriage before giving birth to Aiko.

Rigid and insular palace life is also believed to have contributed to her mental illness.