They are hardened sportsmen, but some professional jockeys have bones as weak as elderly women suffering from osteoporosis.

According to new research, just over half of Irish riders tested have some degree of bone thinning, most likely caused by starving themselves to make the regulation weight for race day. As a result they may be putting themselves at higher risk of fractures when they fall.

“This abnormality in bone metabolism appears to be a result of self-imposed dietary habits to make the regulation weights, and is having a negative impact on the bone health of jockeys,” said the team of doctors who examined them.

One in 20 rides by Irish jockeys results in a fall, one in five of which causes injury to the rider. One quarter of the injuries are bone fractures.

Bone-mineral density was measured in 27 jockeys licensed in Ireland. Of these, 14 (52%) had a score below -1, indicating they had either osteopenia, a less severe reduction in bone mass, or osteoporosis. The research also found a high rate of bone fractures in the jockeys examined. On average the riders had 3.2 previous fractures, with breaks more common in jump jockeys than flat riders. Their diets were found to be deficient in energy, calcium, and vitamin D.

Jockeys have to make weights of between 52.7kg (8st 4lb) and 64kg for flat racing, and 62kg and 76kg for jump racing in Ireland. As this can be up to two stone less than their natural weight, jockeys consume far less than the recommended minimum calories for a sedentary person despite being very active. There can be a deficit of almost 2,000 calories in their daily intake.

Frank Waldron-Lynch, a specialist in endocrinology based at Yale who was involved in the study, said: “The current weights are based on data from the early 20th century. The average population in the 1900s was far lighter than now, so to achieve the weights recommended by the racing organisations is more difficult because jockeys are healthier and have more weight to start with.”

Adrian McGoldrick, senior medical officer for the Irish Turf Club, who was in Cheltenham last week where jockeys such as Paul Carberry suffered falls, was also involved in the research, published in Osteoporosis International.

“We think it’s because they have never laid down their full bone mass, because they’ve been starving since the age of 14 or 15,” he said. “How little they eat is quite frightening. I remember sitting down for dinner one night with two jockeys and they shared one fish.”

In an earlier survey by McGoldrick, 60% of jockeys said they were hungry or thirsty all the time. It recommended to the Turf Club that the minimum weights be raised by 7lb. However, they were increased by 4lb, giving Ireland the highest minimum weights for jockeys in Europe.

However, McGoldrick said an increase of a pound a year was needed in the lowest weights. He said: “The problem is our horses go racing in England and France so all nations need to agree to up the weights. You just have to see the size of the apprentices coming through — they’re big guys.”

The Irish Turf Club has been receptive to these arguments and employs a nutritionist and physiotherapist to advise riders. However, the British Horseracing Authority refused a request from its chief medical officer to raise its weight limits, which are lower than Ireland’s.

Andrew Coonan of the Irish Jockeys’ Association said: “The Turf Club medical officer works very closely with the riders and assesses any weight problems.”

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