Vitamin D for Bone Health and Immunity: A UK-Focused Guide
Maintaining strong bones and a robust immune system becomes increasingly important as we age. Vitamin D plays a central role in both of these processes. In the UK, where sunlight is often insufficient to meet our vitamin D needs, deficiency is surprisingly common, and misconceptions about the vitamin persist. This article explains how vitamin D supports bone health and the immune system, describes the different effects in children and older adults, and provides practical advice based on reputable UK guidance. Internal links throughout the article will help you explore other topics in our vitamin D series, such as deficiency symptoms, recommended dosages and the best sources.
How Vitamin D Supports Bone Health
Essential for calcium and phosphate absorption
Vitamin D is not a typical vitamin; it functions as a hormone that helps the body absorb calcium and phosphorus from food. These minerals are essential for building and maintaining strong bones and teeth. The British Dietetic Association (BDA) notes that vitamin D allows your body to take in calcium and phosphorus, which are needed for healthy teeth and bones[1]. Without enough vitamin D, calcium absorption falls, leading to low blood calcium and subsequent release of calcium from bone stores.
Preventing osteomalacia and rickets
Bone mineralisation relies on adequate calcium and phosphate. Patient.info explains that normal bone mineralisation depends on adequate calcium and phosphate maintained by vitamin D[2]. When vitamin D is lacking, the mineral content of bone falls, causing soft, poorly mineralised bone tissue. In adults this condition is called osteomalacia, while in children the same process leads to rickets, a disorder where bones are weak and soft[2]. The NHS reports that rickets occurs when a child’s bones become weak and soft, usually due to a lack of vitamin D or calcium[3]. Symptoms include bowed legs, pain in the back or legs, swollen wrists and muscle weakness[4].
Adults with osteomalacia may experience bone pain, tenderness and proximal muscle weakness. BDA guidance warns that vitamin D deficiency in adults can lead to soft bones (osteomalacia) and weak bones (osteoporosis) that break easily[5]. Older adults may also suffer falls or fractures due to impaired muscle strength, which is partly regulated by vitamin D.
Vitamin D, osteoporosis and fracture risk
Osteoporosis, a disease characterised by low bone density and fragile bones, is more common in older adults and post‑menopausal women. Although osteoporosis involves many factors (ageing, hormones, genetics and diet), vitamin D deficiency contributes by reducing calcium absorption. The National Diet and Nutrition Survey estimates that around 23 % of adults aged 19–64 and 21 % of those aged over 65 in the UK have low serum vitamin D status[6]. Adequate vitamin D intake, together with calcium and weight‑bearing exercise, is therefore vital to minimise age‑related bone loss. For those already diagnosed with osteoporosis, healthcare professionals may prescribe higher doses of vitamin D alongside calcium to improve bone mineral density. You can learn more about appropriate dosages in our article on daily vitamin D requirements.
Role in Calcium Absorption and Muscle Function
Vitamin D increases intestinal absorption of calcium and phosphate, helping maintain steady blood levels. Without this hormone, only about 10–15 % of dietary calcium and 60 % of phosphorus is absorbed. Vitamin D also influences muscle function; low levels can lead to muscle weakness and reduced postural control. The BDA notes that vitamin D supports nerve function and helps maintain muscle strength to prevent falls[1]. In older adults, muscle weakness is a major contributor to falls and hip fractures. Ensuring adequate vitamin D status helps maintain muscle fibres and neuromuscular coordination.
Vitamin D and the Immune System
Does vitamin D boost immunity?
Beyond its established role in bone health, vitamin D influences the immune system. Vitamin D receptors are present on many immune cells, and laboratory studies suggest that active vitamin D can modulate both innate and adaptive immune responses. UK public health messages reflect these findings cautiously. For example, the St Helens Borough Council explains that vitamin D is needed for healthy bones and muscles and may help support our immune system, advising everyone to consider taking a supplement during winter[7]. Slough Borough Council echoes this advice, noting that taking vitamin D can help improve overall health, prevent bones from weakening and strengthen the immune system to help prevent infection[8].
The BDA also highlights that vitamin D assists your immune system to fight infections[1]. However, evidence that vitamin D supplementation prevents specific infections remains inconclusive. Bupa notes that vitamin D may help keep our immune system strong but we don’t know for certain[9]. Randomised trials have shown modest reductions in acute respiratory infections among those with low vitamin D status, but health authorities caution that supplements are not a substitute for vaccinations or other public health measures. Our focus should be on maintaining adequate vitamin D levels through safe sun exposure, diet and supplements to support normal immune function.
Vitamin D and COVID‑19
During the COVID‑19 pandemic, researchers investigated whether vitamin D could reduce infection severity. While some observational studies suggested an association between low vitamin D levels and worse COVID‑19 outcomes, high‑quality evidence remains limited. The NHS states there is not enough evidence to support taking vitamin D solely to prevent or treat COVID‑19[10]. Nonetheless, Public Health England and the NHS advised everyone to take a daily 10 µg supplement during the autumn and winter months when sunlight is weak[11]. Taking the recommended supplement ensures that your immune system has the vitamin D it needs to function normally.
Effects in Different Age Groups
Babies and children
Growing bones require adequate vitamin D to mineralise properly. Without it, children develop rickets, resulting in bone deformities, poor growth and muscle weakness. BDA guidance notes that children who don’t get enough vitamin D can develop rickets, which causes bone deformity, weak muscles and poor growth[12]. The Department of Health and Social Care therefore recommends that:
- Breastfed infants aged 0–1 years receive 8.5–10 µg (340–400 IU) of vitamin D daily[13].
- Children aged 1–4 years receive 10 µg (400 IU) daily[13].
Formula‑fed babies who drink more than 500 ml of fortified formula each day usually receive enough vitamin D through the formula and do not need extra supplements[14]. Parents and carers should consult their health visitor or GP if they are unsure about supplementation. The Healthy Start scheme provides free vitamin D supplements to eligible families.
Adults and older adults
From adolescence onwards, vitamin D remains crucial for bone maintenance and muscle function. Adults and children over 4 years are advised to consider taking a 10 µg supplement during the autumn and winter[15]. People in high‑risk groups—those with darker skin, limited sun exposure, high body mass index, malabsorption or chronic liver/kidney disease—should take 10 µg year‑round[16]. Adults aged over 65 often have reduced skin synthesis and may spend less time outdoors; deficiency in this group is common and increases the risk of falls and fractures. Public health messages stress that vitamin D helps maintain muscle strength, thereby reducing fall risk[1]. In St Helens, the Director of Public Health notes that too little vitamin D can lead to bone problems such as rickets in children and bone pain and muscle weakness in adults, which may also increase the risk of falls in older people[17]. Ensuring sufficient vitamin D intake through supplements and diet is therefore important for preserving mobility and independence in later life.
FAQs about Vitamin D for Bones and Immunity
Can I get enough vitamin D from sunlight alone? During UK spring and summer (April–September), you can make vitamin D by exposing your skin to midday sun for short periods without sunscreen. However, between October and March, sunlight is too weak for vitamin D synthesis[18]. People with darker skin, the elderly or those who cover their skin may need longer exposure and should not rely on sunlight alone. For detailed guidance on safe sun exposure and sources of vitamin D, see our article on top sources of vitamin D.
Does vitamin D improve my immune system enough to skip vaccinations? No. Vitamin D supports normal immune function but it does not replace vaccinations or other preventive measures. Local councils advise taking vitamin D alongside getting your flu and COVID‑19 vaccines[19]. Supplements are part of a broader approach to health rather than a standalone cure.
Is it possible to take too much vitamin D? Yes. While 10 µg (400 IU) daily is safe for most people, large doses over 100 µg (4,000 IU) can cause toxicity, leading to high blood calcium, nausea and kidney damage. Always follow your doctor’s instructions, especially if you have medical conditions or are taking other supplements[20].
How can I include vitamin D in my diet? Few foods naturally contain vitamin D. Oily fish (salmon, sardines, herring), egg yolks, red meat, liver and some mushrooms provide small amounts[21]. Many cereals, plant milks and spreads are fortified. However, even a balanced diet usually cannot provide enough vitamin D, so a supplement is recommended during the darker months.
Do other nutrients affect bone health? Yes. Adequate calcium, protein, magnesium and vitamin K are also essential for bone strength. Weight‑bearing exercise (such as walking, dancing or weight‑training) stimulates bone formation. For more detailed advice on diet and lifestyle factors, speak to a dietitian or visit our vitamin D guide.
Conclusion
Vitamin D is pivotal for building and maintaining strong bones and supporting immune and muscle function. In the UK, lack of sunlight and limited dietary sources make deficiency common across all age groups. Ensuring adequate intake protects children from rickets, prevents osteomalacia and osteoporosis in adults, reduces fall risk in older people and supports normal immune responses. Public health organisations recommend that most people in the UK take a 10 µg supplement during autumn and winter, and high‑risk groups should continue year‑round[15]. Pair this with a balanced diet, safe sun exposure and regular exercise for optimal bone and overall health. For related information on symptoms of deficiency, recommended doses and sources of vitamin D, explore our other articles on this site.
- What is Vitamin D and Why It’s Essential – Basic overview of vitamin D and its role in the body.
- Symptoms and Risks of Vitamin D Deficiency -Detailed discussion of signs, health risks and when to get tested.
- Vitamin D3 vs D2: Which Is Better? – Compare structure, absorption and sources.
- How Much Vitamin D Do You Need Daily? -Age‑specific dosage recommendations and special considerations.
- Top Sources of Vitamin D (Food, Sun, Supplements) – Practical tips for obtaining vitamin D safely and effectively.
- Vitamin D for Bone Health and Immunity – Explore how vitamin D supports bones and immune function.
- Who is Most at Risk for Vitamin D Deficiency in the UK? – Identify high‑risk groups and tailored solutions.
References
[1] [5] [12] [15] [16] [20] [21] Vitamin D – BDA
https://www.bda.uk.com/resource/vitamin-d.html
[2] [6] [13] [14] Vitamin D Deficiency including Osteomalacia and Rickets
https://patient.info/doctor/vitamin-d-deficiency-including-osteomalacia-and-rickets-pro
[3] [4] Rickets and osteomalacia – NHS
https://www.nhs.uk/conditions/rickets-and-osteomalacia/
[7] [17] [18] [19] Residents urged to boost Vitamin D intake and keep well in Winter – St Helens Borough Council
[8] [11] Have you taken your Vitamin D today? – Slough Borough Council
https://www.slough.gov.uk/news/article/39/have-you-taken-your-vitamin-d-today
[9] Vitamin D: what you need to know
https://www.bupa.co.uk/newsroom/ourviews/vitamin-d
[10] Vitamin D – NHS
https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/