3 January 2014 Last updated at 17:34 GMT

Vitamin D 'boosts child muscles'

Higher levels of maternal vitamin D during pregnancy have been linked to better muscle development in children, say researchers.

The study on 678 children, published in Endocrine Research, showed vitamin D levels in the womb were linked to grip strength at the age of four.

The team at the University of Southampton say the muscle boost could persist throughout life.

Trials are taking place to see how effective pregnancy supplements are.

Most vitamin D is made by the skin when exposed to sunlight and supplements are offered during pregnancy.

Some doctors have voiced concerns about vitamin D deficiency as people become more "sun aware" and have linked it with a range of health problems.

Hold tight

The team at the University of Southampton investigated the impact of the vitamin in pregnancy.

Blood samples were taken 34 weeks into the pregnancy and the vitamin D levels were compared with how tightly their children could squeeze a device in their hand at the age of four.

The results showed that women with high levels of vitamin D in the late stages of pregnancy were more likely to have children with greater muscle strength.

Dr Nicholas Harvey told the BBC that: "There's some evidence that 'fast' muscle fibres go down in vitamin D deficiency and you get more fat in muscle.

"If there is deficiency in utero then they may end up with a lower number of numbers of these 'fast' muscle fibres."

The group in Southampton is now conducting a trial in which 1,200 expectant mothers are given higher doses of vitamin D supplements to assess the impact on both bone and muscle strength.

Dr Harvey said there may be long term benefits to increasing muscle strength.

"It peaks in young adulthood before declining in older age and low grip strength in adulthood has been associated with poor health outcomes including diabetes, falls and fractures.

"It is likely that the greater muscle strength observed at four years of age in children born to mothers with higher vitamin D levels will track into adulthood, and so potentially help to reduce the burden of illness associated with loss of muscle mass in old age."

Prof Cyrus Cooper, from the Medical Research Council Lifecourse Epidemiology Unit, added: "This work should help us to design interventions aimed at optimising body composition in childhood and later adulthood and thus improve the health of future generations."