The Emperor and Empress of Japan may shortly be forced to cut back on their official duties because both are apparently suffering from failing health.

Amid signs that the ruler of the Chrysanthemum Throne is no longer able to maintain his usually active schedule, the Emperor’s eldest son, Crown Prince Naruhito, said over the weekend that his parents needed “more time for rest”.

The couple remain highly active, despite the advancing years of the Emperor and Empress: they travel widely within Japan, and are regular visitors to regions stricken by the country’s annual toll of earthquakes.

Local media reports suggest that Emperor Akihito, 74, could be suffering the early effects of osteoporosis and needs a “lifestyle adjustment” to prevent the condition worsening.

It is thought that the bone-thinning condition may be a side-effect of his treatments for prostate cancer, which included surgery in 2003 and hormone therapy afterwards.

According to the public broadcaster, NHK, the Emperor’s cancer remains in check, though his bone density has fallen sharply. Empress Michiko, who is a year younger than her husband, has recently been suffering from dizzy spells and intestinal bleeding, though health checks suggest she is not suffering from a life-threatening condition.

The revelations of the Emperor’s declining health follow recent hints of a spiralling family row between him and the Crown Prince.

The hints, in keeping with the obsessive privacy of Japanese royal tradition, are almost undetectable in their subtlety.

But a promise by Crown Prince Naruhito ahead of his 48th birthday that he would visit his parents more often - is viewed by close palace observers as evidence of a three-way power struggle between a father, a son and the notoriously conservative bureaucracy that runs the Imperial palace.

The same observers said that the atmosphere around the Chrysanthemum Throne was as tense as any of them could remember, and that the Prince’s promise likely represented his yielding to heavy domestic pressure from the Emperor and Empress, who have made it clear that they want to spend more time with their grand-daughter.

The Prince’s promise, which was made at his annual pre-birthday press conference, was merely that he would step-up the frequency of visits to the Imperial palace just a few kilometres away.

But his remarks come just weeks after what appeared to be an extraordinary chiding from the head of the Imperial Household Agency, Shingo Haketa. In a public statement that was striking in its candidness, Mr Haketa said: “I think the Emperor and Empress are concerned because the number of visits [by the Crown Prince's family] to the Imperial Palace has not increased”

Haketa continued his criticism, saying that he wanted Naruhito to “respect” the promise made a year previously to increase the visits. That 2007 was itself a response to a comment by the Emperor, in which he said that it was “unfortunate” that he had so few opportunities to see his grand-daughter, Aiko.

The comments are thought to have been crafted deliberately to echo those in a 1964 press conference by the current Emperor, while he was still the Crown Prince, in which he said he would always honour his promises.

In the space of the past year, Prince Naruhito has been to visit his parents only 15 times. His brother, Prince Akishino, has taken his family to the palace on some 45 occasions.

The Imperial household remains tormented by the continuing illness of the future Empress, Princess Masako, and the four-year “adjustment disorder” from which she has made only minimal recovery. Her illness has symptoms that are similar to depression.

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