The palace recently announced that Emperor Akihito, who is turning 75, is suffering from a stress-related illness that includes an irregular pulse and bleeding from his stomach, a revelation that left the country buzzing with rumors about what ails the emperor.

Some say the head of the world's oldest hereditary monarchy is concerned over the future of the imperial house, others say it is his daughter-in-law's chronic health problems or his own worsening illnesses.

Emperor Akihito underwent an operation for prostate cancer in 2003, and the palace statement released earlier this month said doctors suggested the emperor's official duties be lightened.

'His majesty has felt mental stress over many matters,' Shingo Haketa, the head of the Imperial Household Agency, said in the statement. He did not specify what matters were bothering Emperor Akihito.

Emperor Akihito chose to sit out a news conference he normally holds about a week before his Dec 23 birthday, but palace officials said he will still appear before well-wishers for his annual birthday greetings Tuesday to wave to them three times from a palace verandah.

He is also scheduled to wish visitors a happy new year on Jan 1, but may appear at the window fewer times than usual, a palace official said on Monday on condition of anonymity in keeping with imperial protocol.

The emperor is the latest of Japan's royal family to complain of serious stress.

Though no longer revered as living gods, members of the imperial family live tightly regimented lives and are rarely allowed candid moments in public, making their public appearances highly scripted and giving them little time to relax.

Crown Princess Masako, the emperor's 45-year-old daughter-in-law, withdrew from most of her official duties and appearances several years ago because of a nervous disorder attributed to the difficulties she felt adjusting to palace life and the pressure of expectations that she would bear a son to continue the imperial line.

Empress Michiko, 73, has also often complained of stress and suffered a breakdown in the early 1990s that rendered her unable to speak for months. Last year, she suffered bleeding from the walls of her intestines, nose bleeds and mouth ulcers. The palace said those illnesses were also related to stress.

A succession crisis is also believed to be a major source of worry for the royal family.

Under a post-World War II law, only males are allowed to assume the throne. Princess Masako's husband, Crown Prince Naruhito, is next in line, but they have no sons of their own. When Princess Masako and Prince Naruhito had a daughter, a movement heated up to change the law to allow the girl to succeed her father.

That died down when Prince Naruhito's younger brother, Prince Akishino, had a baby boy two years ago.

Tabloids have speculated that a rift has developed between those who support the boy and those who believe the girl, now 7, should be allowed to reign. -- AP