Is this the reason so many women feel totally clapped out?
Exhausted Melissa went to her GP for blood tests
Pitchfork in hand, I was making a fresh bed in my horse's stable when I suddenly felt so weak I could hardly move.
I shuffled around the stable, pushing the fork lamely until the straw bed looked so inviting I lay down in it and fell asleep. It was 10am - this was ridiculous.
Normally, I walk my dog twice a day and horseride up to four times a week. I spend hours mucking out stables and hauling heavy tack around. I am not used to feeling physically feeble. But a few months ago I was so tired that I found myself going to bed at 8pm some nights and struggling to get up the next morning. Everyday tasks were gruelling.
I was desperately craving sweet treats. Despite not having a sweet tooth, chocolate bars and biscuits were going down at such an alarming rate that, being a terrible hypochondriac anyway, I had started to fear I had diabetes. I had read that some women, even if they are slim and eat healthily, can develop diabetes when they are over 40 if their bodies don't make enough insulin. One of the symptoms is relentless hunger.
I was also picking up infections - nothing serious - but even minor cuts and grazes didn't heal properly. I could have sworn my vision was blurring, too. I was constantly dizzy, and on several occasions had fainted.
I went to my GP and she ordered blood tests. A week later, when she hadn't called back, I phoned the surgery to ask about the results.
The receptionist told me not to worry. There could not be anything wrong because the doctor would have rung if there was. When I insisted that I would like to speak to her anyway, the receptionist said it was 'not protocol' for the doctor to ring a patient unless there was a serious issue with their results.
Feeling troubled, I hung up, and then rang a friend who is a nutritionist. He told me to demand a copy of my results - it was my legal right - as there could easily be something in them pointing to why I felt so ill.
I am very glad I did. When I collected the pathology report the next day, there were exclamation marks next to various blood readings and the lab technician had even taken the trouble to write a warning at the top.
I was seriously deficient in vitamin D. At first, I thought: 'Well, aren't we all?'
We have had such a terrible winter that I was not at all surprised to find that I had depleted levels of the 'sunshine vitamin'. Whereas a normal reading should be 75-200 nanomoles of vitamin D per litre of blood, my reading was just 37.
But that was not all. My white blood cell count was down, showing a depressed immune system. Since my doctor had not so far been forthcoming, I started to do my own research.
When I looked up the link between vitamin D and a low white cell count, I found a study conducted by scientists at Yale University that said when vitamin D levels get low, your immune system can start to suffer.
It revealed that people with high levels of vitamin D fall ill about half as often as people with low levels. And when they do fall ill, they recover more quickly. The research seemed to indicate that vitamin D instructs our white blood cells to manufacture a protein that kills infections.
Vitamin D deficiency wasn't all, her white blood cell count was down, showing a depressed immune system
More amazingly still, the researchers believed that people with high levels of vitamin D run a 30 to 50 per cent lower chance of breast cancer, and a 50 per cent lower chance of colon cancer, because vitamin D regulates some of the genes responsible for cellular growth.
If vitamin D is so essential, why on earth had the doctor not even told me I was deficient?
I followed the advice of the lab technician, written on the test form, which was to take a daily supplement of 1000 units of vitamin D3, which I bought from a local health food shop.
But I was furious my doctor had not rung me, when all that was needed to correct my lethargy, dizziness and fainting spells was a £7.99 bottle of vitamins. And how many more people might be unaware that they have the same problem?
In fact, some doctors believe that Britain is suffering from an epidemic, with as many as nine in ten people deficient in vitamin D. Rickets, a disease which sees the bones soften and fail to form properly, is on the rise in children for the first time since the Victorian era because vitamin D is needed to help build bones.
Lack of sun and the fact that so few children play outdoors any more is to blame.
Scientists say that lack of vitamin D affects the immune system to such an extent that it could play a role in determining how likely we are to develop not only certain forms of cancer, but also tuberculosis, diabetes and multiple sclerosis.
They are also concerned about vitamin D deficiency in the elderly, especially women, fearing that it may contribute to osteoporosis - a thinning of the bones.
Even those of us who eat a healthy and varied diet may not be getting enough vitamin D. To understand why, you need to know that vitamin D is not really a vitamin at all. It is a hormone.
We manufacture it in the body and only 10 per cent of it comes from our diet, while the other 90 per cent is made by our bodies from the action of sunlight on our skin.
'After a month of taking a supplement, I already have more energy'
Various chemicals already in the body are converted into the vitamin by a process in the liver and kidneys. This means sun exposure really is the only way to get enough vitamin D.
According to Dr Rosemary Bland, Associate Professor of Biological Sciences at the University of Warwick, who specialises in vitamin D research, our fear of skin cancer may have inadvertently led to a situation whereby we are causing ourselves other health problems.
'I would like to see education into sunlight exposure. The last thing we would suggest is that anyone get sunburnt, which is very bad. But if you look at your moisturisers and foundations they have all got sunscreen in them, which is good for anti-ageing but stops us absorbing vitamin D,' she says.
'People are not out in the sun at all now without sunscreen, but you could expose your arms and legs, perhaps while cycling to work, for example. People need to get some sunlight or take a supplement. And doctors need to be more aware if people's levels are down.'
All the medical trials on the link between vitamin D and cancer have so far concentrated on administering high doses to cure the disease, with inconclusive results.
However, Dr Bland believes that it is more likely that the vitamin has a preventative effect, as the Yale researchers found.
Until more research and trials are done, government bodies such as NICE (the National Institute for Health and Care Excellence) will not take notice and issue guidelines for GPs. And doctors will not alert patients to low vitamin D levels.
Online, there is plenty of anecdotal evidence of people who claim high doses of vitamin D have transformed their health.
I came across the story of one woman who, after years of seeing various specialists, had doubled her white blood cell count in 14 days by taking high doses of vitamin D.
When I spoke to nutritionist Ian Marber, he told me: 'Get tested and always supplement a healthy diet. Remember, there is no point supplementing a bad diet. I take 1,000 units a day because that is the general consensus.'
After a month of taking a supplement, I already have more energy. I will have another test soon to find out if my white cell count has been boosted. In the meantime, and as the weather improves, I have been rolling up my sleeves whenever we get a few precious hours of sun to top up my vitamin D levels naturally.
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