Science proves that holidays in the sun are the key to happiness

A while ago I found myself in the unusual position, for a travel writer and editor, of being told to get out more. I'd had a sore shoulder, then a sore back, then everything seized up and I began walking around like a faulty robot in a bad science fiction movie. People had begun to stare, so I booked an appointment with a specialist.

Working in travel is always a great conversation starter, and once he'd found out what I did for a living, this specialist was immediately on my case. Where did I recommend going, he asked, while examining my (extremely lopsided) shoulders. Was Croatia too hot in July, he wondered, prodding my aching neck. And could I recommend a decent gîte in Provence?

As he measured and calibrated, poked and stretched, we covered most of the usual European summer holiday destinations, while I winced and moaned a bit. Happily, given all the agonising tweaking, I got the impression he wasn't that interested in my professional opinion, perhaps because he was about to deliver his.

It was nothing too dramatic, he said. I had bad posture and might benefit from a cortisone injection. He would run some blood tests as a precaution. And had I heard good things about Puglia?

Anyway, I did the blood tests and thought no more about it until he asked me to get in touch a week or so later. Everything was fine, he said, apart from one thing: my vitamin D levels. I was "very" deficient apparently, and would be required to stuff myself with quite astonishing amounts of vitamin D3 in supplement form for the next month or so. His final words of advice were, I felt, slightly patronising: "As a travel editor, you need to give yourself some sunny locations to visit."

Medical science tells us that we need sunshine to thrive. I swiftly became an "expert" on this, via the wisdom of the internet. The NHS site revealed that vitamin D helps regulate the amount of calcium and phosphate in our bodies, vital for healthy bones, teeth and muscles. Most of us could do with getting more of it, and if children are badly deficient they get rickets (bone deformities and pain) while adults get the grown-up equivalent: osteomalacia. Crucially though, during summer, we should be able to get all the vitamin D we need from sunlight.

Unless that is you spend all of your daylight hours, as I do, cooped up in an office, and your cycle commute swathed in sun-defying Lycra. Your skin needs to be exposed to ultraviolet rays in order to receive enough energy to make vitamin D, you see. It doesn't work through windows or high-performance fabrics. You need to get out there and, er, expose yourself.

I know what you're thinking: oily fish. But apparently it's hard to get enough vitamin D from food. Yes, it's present in salmon and mackerel, red meat and egg yolks, and your Special K comes fortified with bonus vits, but good old sunlight does the job best.

Vitamin D production isn't the only benefit we gain from the sun's rays: moderate sunlight is also said to improve mood by boosting serotonin levels in the body, which reduces the risk of seasonal affective disorder (SAD). Sunshine tends to make us happier and more optimistic, and holidays add to our joie de vivre as we spend time with our nearest and dearest.