A British summer, even a hot one, is no guarantee of healthy vitamin D. A 2026 Newcastle University study of nearly 300 people in northern Britain found that vitamin D levels stayed low all year round in the groups most at risk: 54.8% of older adults and 72.1% of adults from minoritised ethnic backgrounds were insufficient or deficient, and those rates did not improve during the summer months. So while the UK enjoys another heatwave week, plenty of us are still running low without knowing it. The only way to know your level is to measure it, and a simple vitamin D test (a finger-prick vitamins blood test starts at £69) will tell you exactly where you stand before the darker months arrive.

In this article

• Can you be low in vitamin D during a British summer?
• What are the symptoms of low vitamin D?
• How do you check your vitamin D levels?
• Which vitamin D test is right for you?
• How do you keep your vitamin D topped up?
• Frequently asked questions

Can you be low in vitamin D during a British summer?

Yes. The long-held assumption is that a few sunny months rebuild everyone's vitamin D stores for the year. The Newcastle University research, published in the European Journal of Clinical Nutrition in 2026, challenges that directly. Screening people across northern Britain through every season, the team found that in older adults and in people from minoritised ethnic backgrounds, low vitamin D was just as common in summer as in winter.

The reasons are practical. Skin makes vitamin D less efficiently as we age. Melanin-rich skin needs longer sun exposure to make the same amount. Many of us spend summer indoors, cover up outside, or wear sunscreen (sensible for skin cancer prevention, but it reduces vitamin D production). Latitude matters too: the UK sits far enough north that the window for meaningful vitamin D synthesis is shorter than most people think.

The takeaway is simple: you cannot feel or guess your vitamin D level, and you cannot assume the sunshine has sorted it. Testing removes the guesswork.

What are the symptoms of low vitamin D?

Vitamin D deficiency symptoms are easy to miss because they are vague and build slowly. Common ones include:

• Tiredness and low energy that does not improve with rest
• Aching bones, joints or muscles, often in the back or legs
• Muscle weakness or cramps
• Low mood, particularly through the darker months
• Frequent colds or infections, as vitamin D supports normal immune function

Because these overlap with iron deficiency, thyroid issues and plain modern exhaustion, symptoms alone cannot tell you which is the cause. That is why a blood test that measures several markers at once is usually more useful than guessing at a single culprit. If symptoms are persistent or severe, speak to your GP.

How do you check your vitamin D levels?

A vitamin D blood test measures 25-hydroxyvitamin D, the storage form of the vitamin in your blood, and reports whether you are deficient, insufficient or in the healthy range. The NHS does not routinely test people without symptoms or risk factors, so many people in the UK choose a private test for a clear, numerical answer.

With Goodbody Clinic you can test three ways: a finger-prick kit at home, a quick professional draw at one of 250+ clinics nationwide, or a nurse visit to your home. Results are reviewed and reported clearly, so you know whether your level is where it should be and can discuss next steps with your GP if anything is out of range. You can read more about how home testing works in our guide to blood tests at home in the UK.

Which vitamin D test is right for you?

It depends on how wide you want to look. If you only want vitamin status, a focused vitamins panel is the quickest and cheapest route. If your main complaint is exhaustion, a tiredness panel adds iron and thyroid markers. If you want a full picture of your health in one appointment, a complete panel covers vitamin D alongside dozens of other markers.

Test	What it covers	Best for	Price
Vitamins Blood Test	Vitamin D, B12, folate	A focused vitamin check, at home from a finger-prick kit	From £69
Tiredness and Fatigue Blood Test	Vitamin D plus iron and other common causes of fatigue	Feeling tired all the time and wanting answers	From £139
Premium Complete Blood Test	61 key health markers including vitamin D	A full annual health MOT in one appointment	From £249

How do you keep your vitamin D topped up?

The NHS advises that everyone in the UK should consider a daily 10 microgram (400 IU) vitamin D supplement during autumn and winter, and that people with limited sun exposure or darker skin should consider one all year round. The Newcastle findings suggest that year-round advice matters more than many of us realised.

Alongside sensible sun exposure, dietary sources help: oily fish such as salmon and sardines, red meat, egg yolks, and fortified foods like some cereals and spreads. But food alone rarely supplies enough, which is why the supplement guidance exists. Testing first means you know whether you are correcting a genuine shortfall, and a repeat test a few months later shows whether your routine is working. You can browse the full range of checks in our general health blood tests collection.

Frequently asked questions

How much vitamin D do I need per day?

Adults and children over 4 in the UK need 10 micrograms (400 IU) of vitamin D a day, according to the NHS. Most people cannot reliably get this from food alone, which is why a daily supplement is advised through autumn and winter, and year round for higher-risk groups.

Can you take too much vitamin D?

Yes. Taking more than 100 micrograms (4,000 IU) a day over a long period can cause too much calcium to build up in the body, which can affect bones, kidneys and the heart. You cannot overdose from sunlight. This is another reason to test before taking high-dose supplements.

When should I take a vitamin D test?

Any time works, but late summer is a smart moment: it shows your level at its likely seasonal peak. If you are low now, you are unlikely to improve as autumn arrives, so you can start correcting early. Testing again after 3 to 6 months shows whether your routine is working.

Is vitamin D3 the same as vitamin D?

Vitamin D3 (cholecalciferol) is one of the two main forms of vitamin D, and it is the form your skin makes from sunlight. Vitamin D2 (ergocalciferol) comes mainly from plant sources. Blood tests measure your combined 25-hydroxyvitamin D level, which reflects both forms.

Does sitting by a sunny window help?

No. Glass blocks most UVB, the wavelength your skin needs to make vitamin D, so sunshine through a window does not meaningfully raise your level. Short periods of direct summer sun on bare forearms are far more effective, balanced against sun-safety advice.

Sources: Newcastle University vitamin D study (2026), published in the European Journal of Clinical Nutrition; NHS guidance on vitamin D.

This article is general information, not medical advice, and blood tests indicate rather than diagnose. If you have symptoms or concerns about your health, speak to your GP.