Vitamin D – The One Supplement I Take All Year Round
By Dr Timothy Eden, MBBS and Registered Dietitian
Read time approx. 4-5mins
Why Vitamin D Matters More Than You Think
In the world of nutrition and preventative health, few nutrients have attracted as much attention as vitamin D in recent years and for good reason. Once primarily associated with bone health, we now know that vitamin D plays a much broader role, influencing everything from immune function to muscle strength, mood regulation and potentially even chronic disease risk. Emerging research continues to link low vitamin D levels with a range of health issues, including autoimmune conditions, infections, cardiovascular disease, and even certain cancers.¹ ²
Yet despite its importance, suboptimal levels of vitamin D or even outright deficiency remain surprisingly common and often go unnoticed. Many individuals may not realise they’re lacking it until symptoms such as fatigue, low mood, frequent infections or bone pain begin to emerge. The good news? Vitamin D is safe, inexpensive and easy to supplement. While the scientific literature continues to explore whether low vitamin D levels directly cause these issues or are simply associated with them as markers of poor health, teasing out causation from correlation can be complex. Nonetheless, given its favourable safety profile, low cost and potential benefits this is one supplement that many consider worth taking as a precautionary measure. It’s also the one I personally choose to take all year round.
Who Is at Risk of Low Vitamin D?
1. Skin Tone & Sunlight Exposure
Vitamin D is produced in the skin in response to sunlight but how efficiently we make it depends on our skin type. People with darker skin; including individuals of African, African-Caribbean and South Asian heritage require more sun exposure to produce adequate vitamin D compared to those with lighter skin. This means people with more melanin are at greater risk of suboptimal levels or deficiency particularly when living in northern latitudes like the UK.³
2. Geography & Seasonality
Living in the northern hemisphere means that between October and March, the sun’s UVB rays are too weak in the UK for vitamin D synthesis, regardless of skin tone. During this period we must rely on dietary sources or supplements to maintain healthy levels.
3. Pregnancy & Breastfeeding
Vitamin D requirements increase in pregnancy due to the additional demand of supporting foetal bone development and immune function. Deficiency in pregnancy has been linked to gestational diabetes, low birth weight and skeletal problems in the newborn.⁴ NICE guidance recommends all pregnant and breastfeeding women take a daily 10 microgram (400 IU) supplement. You can get vitamin supplements containing vitamin D free of charge if you're pregnant or breastfeeding and qualify for the Healthy Start scheme.
Other Groups at Higher Risk
Certain health conditions and medications can impair vitamin D absorption or metabolism:
Inflammatory Bowel Disease (e.g. Crohn’s, ulcerative colitis) and coeliac disease can limit absorption in the gut.
Liver and kidney disease affect the conversion of vitamin D into its active form.
Obesity is associated with lower bioavailability of vitamin D due to its sequestration in fat tissue.
Medications such as long-term corticosteroids, anticonvulsants (epilepsy medications) and some HIV treatments can interfere with vitamin D metabolism.
In these cases vitamin D supplementation may not only help improve general wellbeing but may be part of fracture prevention strategies, particularly in those on long-term steroids as per NICE and NHS recommendations which your healthcare professional will help identify and recommend on an individual basis.⁵
How Do We Get Vitamin D?
1. Sunlight
About 90% of our vitamin D comes from sun exposure, with just 10% from food. Exposing forearms, hands or lower legs to sunlight daily for around 10–30 minutes during the warmer months (April–September) can usually produce adequate levels. However, sunscreen use, clothing, air pollution and time spent indoors all reduce synthesis.
2. Dietary Sources
Vitamin D is naturally present in relatively few foods, including:
Oily fish (e.g. salmon, mackerel, sardines)
Egg yolks
Liver
Red meat
Fortified foods – such as breakfast cereals, yoghurt/dairy products, plant-based milk alternatives, and margarine
Many people in the UK do not get enough from food alone which is why fortification is becoming increasingly important, particularly for plant-based or vegetarian diets.
UK Guidelines & Supplementation Advice
The NHS and SACN recommend that:
All adults and children over 4 years take a daily supplement of 10 micrograms (400 IU), especially during autumn and winter.
Those at higher risk of deficiency (e.g. people with darker skin, housebound individuals, those who cover up for cultural reasons, pregnant and breastfeeding women) should consider year-round supplementation.⁶
Infants and children under 4 should also be given vitamin D drops unless they consume over 500ml of infant formula daily (as this is already fortified).
Supplements are readily available over the counter as tablets, sprays, or drops. Vitamin D3 (cholecalciferol) is usually preferred over D2 (ergocalciferol) for better absorption.
Final Thoughts: Why I Take Vitamin D All Year
Vitamin D is one of the few supplements with a strong evidence base, a favourable safety profile, and wide-ranging health benefits. It supports immune health, helps maintain bone and muscle strength and may contribute to mental wellbeing with potentially more benefits likely to emerge as research continues.
Given the low cost, accessibility and the fact that many of us are at risk of deficiency without knowing it, I consider it a simple and effective step towards better health. That’s why I take it every day.
If you’re unsure about your vitamin D status or whether you may benefit from supplementation, it’s always wise to speak to your GP, dietitian or another qualified healthcare professional. Testing may be advised in certain cases, particularly if you have symptoms or fall into a higher-risk group.
References:
SACN (2016). Vitamin D and Health. Scientific Advisory Committee on Nutrition.
NICE CKS. (2023). Vitamin D deficiency in adults – treatment and prevention.
National Institute for Health and Care Excellence (NICE). Vitamin D: supplement use in specific population groups [PH56]
Royal College of Obstetricians and Gynaecologists. (2014). Vitamin D in Pregnancy.
NHS. Who should take vitamin D supplements? – nhs.uk
BDA – British Dietetic Association. Vitamin D Food Fact Sheet