Women due to give birth in winter should use a sun lamp during the final three months of pregnancy to protect their child from osteoporosis in later life, doctors have suggested.

They made their recommendation as research found that children born to mothers whose final three months of pregnancy included a summer month were 40% less likely to suffer the bone-wasting condition in adult-hood.

A mother’s exposure to sunlight in that final period ensures the developing baby receives enough vitamin D to form strong bones.

Doctors suggest that women whose last trimester of pregnancy does not fall between May and September should consider taking a holiday in the Mediterranean.

As flying is not advised in the late stages of pregnancy, however, they suggest that women may need to settle for a sun lamp or vitamin D supplements.

Dr Marwan Bukhari, a consultant rheumatologist at the Royal Lancaster Infirmary and author of the study presented to the British Society for Rheumatology, said: “You only get good sunlight [when you make vitamin D] between May and September in this country. Pregnant women should have vitamin D supplements or should have lots of good sunshine in somewhere like north Africa or the southern Mediterranean [in winter].”

Bukhari added: “Sun lamps are an option. It needs to be the right kind of sun lamp to convert fat under the skin to vitamin D.”

The doctors are not recommending sunbeds, which give a far higher dose of ultraviolet light than lamps.

Bukhari and colleagues studied 17,000 patients, mostly women and 95% of whom were white. They had all had scans carried out at the Royal Lancaster Infirmary between 1992 and 2004.

They found that patients under 50 were 40% less likely to have developed osteoporosis if their mother’s last trimester of pregnancy included a summer month.

Older patients were 20%-40% less likely to have osteoporosis if their mothers’ late stages of pregnancy were in the summer.

The study will revive the debate over whether excessive caution about exposure to sunshine is creating other health problems.

Michael Holick, professor of medicine at Boston University in America, said a lack of vitamin D, caused by overzealous avoidance of the sun, was leading to thousands of unnecessary cancer deaths each year and increasing vulnerability to rickets.

Bukhari said: “You could get skin cancer from a sun lamp but not if you use a judicious amount. An hour a month will not give you skin cancer.”

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