Poppy Brett thought she would just have to accept that her son Jago didn't have the energy to keep up with his friends, didn't like playing football and always seemed tired.
Their GP could find nothing wrong with him: he slept 12 hours a night and had a healthy diet. It never occurred to his mother that the factor 25 sun cream she slathered on him in the summer might be to blame for his exhaustion.
But a year ago a blood test revealed that Jago, 11, was severely deficient in vitamin D - vital for maintaining healthy bones and a well-functioning nervous system. Our bodies must have direct sunlight to produce it.
© John LawrenceFull of beans: Jago and his mother Poppy, enjoying the spring sunshine
Twelve months on, after taking supplements and having more exposure to the sun, Jago is a different boy. The lethargy has gone - he loves playing in the park with his friends.
Gone, too, are the pains in his legs that would often cause him to wake in the night in agony. They had been dismissed as growing pains.
'I never thought in a million years that his tiredness could be down to a lack of sun,' says Poppy, 41, a charity fundraiser from Bristol. 'When camping in Cornwall, I'd cover Jago in sunscreen the moment the sun came out.'
Poppy first went to the GP about Jago's leg pains when he was seven, but the doctor simply showed him some stretching exercises. When this failed to have any effect, she went back to the GP twice, but the only suggestion was that he should get more sleep.
'It was utterly frustrating trying to get anyone to take me seriously,' says Poppy. 'Jago looked tired all the time, but they just told me to put him to bed earlier, which was crazy as he was sleeping 12 hours a night.
'I suggested it might be related to his dust-mite allergy, so they suggested I vacuum the house more!'
In February last year, Jago burst into tears at the side of a swimming pool because he felt so unwell. Poppy marched back to the GP and demanded a blood test.
© John LawrenceSunshine kid: Poppy never realised that covering her son with suntan lotion could lead to a vitamin D deficiency
I said: ''Look, there must be something wrong with him. Please can you test his blood?'' It seemed a good place to start.' And she was right.
The results showed Jago's vitamin D level was a quarter of what it should have been - this result was so worrying that the GP arranged for his legs to be X-rayed to check he didn't have the bone-softening disease, rickets. Fortunately, he didn't.
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