For the most part, I think I'm pretty healthy. By no means am I running half-marathons every weekend or busting a gut inHIIT workouts, but I go to the gym regularly, eat my five-a-day (most of the time), and generally dodge the chocolate aisle when dropping into the supermarket.

But when Bluecrestgave me the chance to undergoa full-body 'health MOT', I knew I could find out for sure. The UK-based private health firm offers thorough assessments of your overall well-being at 15,000 locations across the UK, priced from £169 to £319.

Through a series of physical examinations, blood analysis and even an ECG, its experts can then provide detailed information on everything from your heart disease and stroke risk, to calcium and iron concentrations. The main goal is to highlight any underlying issues before they become serious, with prevention at the heart of their approach.

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After taking my own assessment in Southampton, Hampshire, I was relieved to discover that 58 of 82 measured factors were considered 'green' - or good. My cholesterol levels were healthy, my heart rhythm was normal, and my 'biological age' was 18, seven years younger than my actual age.

But one glaring factor fell into the 'red flag' category - and it was something I had never really considered. To my surprise, I am notably deficient in vitamin D, a nutrient crucial for immune function and bone health.

While50 nmol/L of vitamin D in the blood is considered sufficient for most people, my measurements were 35 nmol/L, putting me at greater risk of various unpleasant symptoms. Yet, perhaps surprisingly, it isn't really an uncommon problem.

Figures from Cleveland Clinic suggest that around one billion people worldwide are deficient in vitamin D, including infants, children and adults. Dr Martin Thornton, Chief Medical Officer at Bluecrest, also explained that such deficiencies are especially common in the UK due to several factors, including the weather.

In an interview after my health MOT, he said: "A level of 35 nmol/L indicates vitamin D deficiency, which is essential for various functions within the body, including bone health, immune function and cell growth and differentiation. In the UK, low vitamin D levels are fairly common due to indoor lifestyles and lack of sunlight.

"The good news is that vitamin D deficiency can usually be addressed through a combination of safe sun exposure, dietary changes, and supplementation where needed."

Although vitamin D deficiencies often show no symptoms, they can sometimes cause fatigue, bone pain, muscle weakness, or mood changes such as depression. A severe vitamin D deficiency can also lead to bone deformities such as rickets in children or osteomalacia, a painful condition in adults.

Like Dr Thornton, the UK Government and the NHS advise that diet and supplements play a major role in preventing deficiency, especially during the winter months. Still, you should not take more than 100 micrograms (4,000 IU)of vitamin D a day, as this could be equally harmful.

Official advice in my MOT report further explained: "Good sources of Vitamin D include: Oily fish – such as salmon, sardines, herring and mackerel, red meat, liver, egg yolks, fortified foods – such as some fat spreads and breakfast cereals. To maintain optimal vitamin D levels, check the packaging on the foods you're eating and try to consume around 10 micrograms (400 IU) per day."

Meanwhile, Dr Thornton continued: "While diet helps, vitamin D levels are strongly influenced by sunlight exposure and how well your body absorbs and processes vitamin D. Factors such as limited sun exposure, darker skin pigmentation, geographic location, seasonal changes, or medical conditions affecting absorption or metabolism can all contribute to low levels, even with a good diet."

Although not an official diagnosis, my vitamin D results have certainly encouraged me to rethink my diet, and I've even started taking supplements. Without the MOT, I wonder what problems it may have caused down the line.

If you want to schedule your own health MOT, use Bluecrest's online search tool to find your nearest clinic. There are 15,000 clinics across 400 locations in the UK.