Every spring, the same question appears in millions of Google searches: Do I still need to take Vitamin D now that it is getting sunny? The NHS recommends supplementing from October to March; the days are getting longer and it feels counterintuitive to keep taking a supplement when the sun is finally out.
However, the honest answer is it depends on who you are. For some people, stopping Vitamin D in summer is perfectly reasonable. For a significant proportion of the UK population, it is not and understanding the reasons why will help you make the right decision for your circumstances.
The NHS currently recommends that adults and children over one year consider taking a 10 mcg (400 IU) Vitamin D supplement between October and March, when sunlight in the UK is insufficient for skin synthesis. For the rest of the year, the guidance suggests that most people should be able to get what they need from sunlight. The Scientific Advisory Committee on Nutrition (SACN) published this framework in 2016 and it remains current guidance.
However, the same guidance also notes that certain groups should consider supplementing year-round and that the general 'get sunlight in summer' advice rests on assumptions that do not hold for a significant portion of the UK population.
Continue learning about the importance of vitamin d.
The advice to get sunlight is not wrong in principle, Vitamin D synthesis from UVB radiation is a real and important mechanism. The issue is that the conditions required for meaningful synthesis in the UK are considerably more specific than most people realise. You need direct, unfiltered UVB light on a significant area of skin for a meaningful period of time. On many UK summer days, those conditions simply are not met.
Discover the signs of Vitamin D deficiency.
When ultraviolet B radiation from the sun hits the skin, it converts a molecule called 7-dehydrocholesterol, which is present in skin cells, into pre-Vitamin D3. The liver then converts this into 25-hydroxyvitamin D, the storage form measured in blood tests and the kidneys convert that into the active form, 1,25-dihydroxyvitamin D, which is the version that actually functions in the body.
The key point is that only UVB radiation triggers this conversion. UVA radiation, which is present throughout the year and passes through cloud and glass, does not drive Vitamin D synthesis, it only contributes to skin ageing and damage. The distinction matters because many people assume any daylight exposure is beneficial for Vitamin D, which is not the case.
The intensity of UVB radiation reaching the ground is determined by the angle of the sun. When the sun is low in the sky - early morning, late afternoon, or during winter months , UVB has to travel through significantly more of the atmosphere before reaching the ground and much of it is filtered out. Meaningful Vitamin D synthesis requires a UV index of at least three, which in the UK is only reliably achieved from approximately April to September and only between roughly 11am and 3pm on days with meaningful direct sunshine.
To make this tangible: London sits at approximately 51 degrees North. Madrid sits at 40 degrees North. The equator sits at zero. The further north you are, the lower the sun angle and the thinner the UVB reaching the ground. In Scotland, at 55 to 58 degrees North, the effective window for synthesis is even shorter than in England. In northern Europe, meaningful skin synthesis is not a year-round option even in summer, the geometry of the planet makes it impossible.
NHS England data shows that approximately one in five UK adults has low Vitamin D levels. That figure does not disappear in summer. The latitude issue is part of the explanation, but it combines with a set of lifestyle and physiological factors that mean many people do not spend meaningful time in peak-UVB sunlight even during the months when it is theoretically available.
Most people with conventional working patterns do not have regular access to direct midday sun during the working week. If you commute, work indoors, eat lunch at your desk and commute home, you may spend very little time in direct sunlight during the 11am to 3pm window when synthesis is actually possible, even in July. On weekends, you may catch more sun, but the synthesis from occasional weekend exposure may not be sufficient to maintain adequate levels across the whole week, particularly if you use sunscreen, wear clothing that covers your arms and legs, or spend time in the shade.
Cloud cover does not block UVA, which is why it is possible to burn on an overcast day. But cloud cover does significantly reduce UVB and on the grey, overcast summer days that are entirely normal in the UK, synthesis is minimal. Glass blocks UVB almost entirely, sitting next to a sunny window does not produce Vitamin D. And sunscreen, when used correctly at the SPF required to provide meaningful UV protection, significantly reduces UVB penetration. This does not mean you should not wear sunscreen, sun protection is important and skin cancer prevention is a genuine health priority. It does mean that SPF use reduces Vitamin D synthesis and this should factor into your thinking.
For someone working a standard office job in a UK city, the realistic Vitamin D synthesis opportunity on a weekday is close to zero. The commute may involve outdoor time, but typically not at the angle, duration, or skin exposure level required for synthesis. This is the lived reality for a substantial proportion of the UK workforce and it means that the 'get it from summer sun' assumption does not apply to them.
Melanin, the pigment that gives skin its colour, absorbs UVB radiation. This is one of its protective functions; it reduces UV damage to skin cells. But the same absorption that protects against UV damage also reduces UVB-driven Vitamin D synthesis. People with darker skin tones require significantly longer sun exposure to produce the same amount of Vitamin D as someone with lighter skin; some research suggests six to ten times longer under equivalent conditions. For people with melanin-rich skin living at UK latitudes, where the peak UVB window is already narrow, year-round supplementation is not just advisable but often necessary to maintain adequate levels.
As discussed above, anyone whose working pattern means limited access to midday sun during the April to September window should consider continuing to supplement through summer. This includes most office workers, healthcare workers on indoor shifts, people who work from home and do not spend meaningful time outdoors during peak hours and carers with limited outdoor time.
Consistent SPF use is sensible for skin health. It does, however, reduce Vitamin D synthesis. If you are thorough and consistent with sunscreen application, you should factor this into your Vitamin D strategy, particularly if you are also working indoors during peak hours. Also, check the ingredients in your sunscreen as you are absorbing them, even though it is through your skin.
Skin synthesis of Vitamin D decreases with age, meaning older adults produce less Vitamin D from equivalent sun exposure than younger adults. Combined with the fact that older adults often spend less time outdoors and are more likely to cover up, the case for year-round supplementation in this group is strong. The NHS already recommends this explicitly for care home residents.
If you have had a blood test and been told your Vitamin D is low, or if you have a condition that affects nutrient absorption, e.g., Crohn's disease, coeliac disease, or conditions requiring fat malabsorption medication, you should continue supplementing year-round and may require doses higher than the standard 400 IU recommendation.
Vitamin D is essential for calcium absorption in the gut; without adequate Vitamin D, even a calcium-rich diet will not maintain bone density effectively. This is the most established function and the reason the NHS prioritises it. Beyond bone health, Vitamin D plays a significant role in immune modulation, supporting both the innate immune response (the rapid, non-specific response to pathogens) and the adaptive immune system. Muscle function is also Vitamin D-dependent and deficiency is associated with muscle weakness and increased fall risk in older adults.
The relationship between Vitamin D and mood is an area of active and growing research. Vitamin D receptors are present throughout the brain, including in regions involved in mood regulation and cognitive function. Population studies consistently show associations between low Vitamin D levels and increased rates of depression and seasonal affective disorder.
The NHS recommendation of 10 mcg (400 IU) daily is a safe, conservative threshold appropriate for the general population. For individuals in the higher-risk groups described above eg people with darker skin, those who work indoors, people over 65, or those with known deficiencies, many practitioners and nutrition specialists suggest that 25 mcg (1,000 IU) daily provides a more meaningful level of repletion, particularly through the winter months. Blood levels should be assessed before significantly higher doses are considered, as Vitamin D is fat-soluble and accumulates in tissue. Dosages up to 4,000iu are beneficial.
Vitamin D supplements come in two forms: D2 (ergocalciferol, derived from plants or fungi) and D3 (cholecalciferol, which is the form produced by skin synthesis and traditionally derived from lanolin). Research consistently shows that D3 is more effective at raising and sustaining blood 25-hydroxyvitamin D levels than D2 at equivalent doses. For vegans, algae-derived Vitamin D3 is now available and provides the same form as lanolin-derived D3 without animal involvement. DR.VEGAN's Vitamin D3 is produced from algae for this reason.
Vitamin D increases the body's absorption of calcium from food. But absorbed calcium needs to be directed appropriately to bone rather than to soft tissues and blood vessel walls, where calcium deposition contributes to arterial stiffness. Vitamin K2, specifically the MK-7 form, activates proteins called osteocalcin and matrix Gla protein that direct calcium into bone and away from arteries. D3 and K2 work synergistically: D3 promotes calcium absorption, K2 ensures it ends up where it is needed. This is the clinical rationale for combined D3+K2 formulations and represents a meaningful upgrade over D3 alone for people prioritising bone and cardiovascular health.
The most reliable way to know whether you need to supplement (and at what dose) is a 25-hydroxyvitamin D blood test. This can be requested through your GP, though availability on the NHS varies by region and is typically prioritised for high-risk groups. Private blood tests are widely available and relatively inexpensive, typically between fifteen and thirty pounds. A result below 50 nmol/L is generally considered deficient. Between 50 and 75 nmol/L is considered insufficient. Above 75 nmol/L is considered adequate and many nutrition specialists suggest 100 to 150 nmol/L as an optimal range for most adults.
The DR.VEGAN® Vitamin D3 + K2 combines 2,000 IU of algae-derived D3 with 100 mcg of Vitamin K2 in the MK-7 form, providing the synergistic combination described above. Both are vegan, free from unnecessary additives and produced to DR.VEGAN's quality standards.
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