Vitamin D deficiency.

Why vitamin D matters

Vitamin D is a hormone, not just a vitamin. It’s produced in the skin in response to UV-B sunlight and also obtained from certain foods. It regulates calcium and phosphorus metabolism (and so bone health), but it’s also involved in immune function, muscle function, mood regulation, and cellular processes throughout the body.

Adequate vitamin D matters for:

• Bone health — preventing osteomalacia (adults) and rickets (children); reducing osteoporotic fracture risk
• Muscle function — preventing muscle weakness, falls in older adults
• Immune function — respiratory infection rates, some autoimmune patterns
• Mood — observational links with depression, especially seasonal
• Pregnancy — bone development, immune programming of the foetus

Who’s at risk?

Most people in the UK fall short of optimal vitamin D in winter (October to March), when our latitude means insufficient UV-B reaches us. Higher risk for:

• People with darker skin — melanin reduces vitamin D synthesis in the skin
• People who cover their skin for religious or cultural reasons
• People who don’t spend time outdoors — office workers, indoor-bound, housebound
• Older adults — reduced skin synthesis with age
• People who wear sunscreen consistently — SPF reduces vitamin D production
• Vegans and people who don’t eat fish — limited dietary sources
• People with malabsorption conditions — coeliac, Crohn’s, post-bariatric surgery
• Obese individuals — vitamin D is sequestered in fat tissue
• Pregnant women — increased requirements
• Exclusively breastfed infants
• Some medications — certain epilepsy medications, steroids

Symptoms of deficiency

Vitamin D deficiency often causes vague, non-specific symptoms easily attributed to other things:

• Fatigue, tiredness despite adequate sleep
• Muscle aches and weakness, particularly in legs
• Bone pain — particularly in spine, ribs, pelvis (osteomalacia)
• Joint pain
• Low mood, particularly in winter
• Frequent respiratory infections
• Poor wound healing
• Hair thinning
• Children: growth issues, delayed milestones, bone deformity (rickets)

Many people are completely asymptomatic at moderate deficiency — identified only on testing. Severe deficiency causes more recognisable bone and muscle symptoms.

Understanding vitamin D levels

Vitamin D status is measured by serum 25-hydroxyvitamin D (25(OH)D). UK reference ranges:

• Below 25 nmol/L — deficient. Treatment indicated.
• 25–50 nmol/L — insufficient. Treatment usually indicated, especially if symptomatic.
• 50–75 nmol/L — replete by NHS standards. Maintenance supplementation may still benefit some.
• 75–125 nmol/L — optimal for most clinical outcomes per current evidence
• Above 125 nmol/L — high. No additional benefit; toxicity becomes a consideration above 250 nmol/L sustained.

There’s ongoing debate about optimal levels. NICE recommends 50 nmol/L as the cutoff for sufficiency; some researchers and clinicians target higher (75–100 nmol/L). We discuss what’s reasonable for you.

How we assess at MHW

1. Brief consultation

For straightforward vitamin D testing, a short consultation to confirm test indication, discuss your risk factors and any symptoms.

2. Blood test

25(OH)D blood test. Sometimes alongside related tests:

• Calcium and phosphate
• Parathyroid hormone (PTH) — rises with chronic deficiency
• Liver and kidney function (affect vitamin D metabolism)
• Other nutritional markers depending on the picture

Results typically back within 2–5 working days.

3. Interpretation and plan

Discussion of results, what they mean for you, what supplementation if any, and when to retest.

4. Follow-up

Retest typically at 3–6 months after starting replacement to confirm adequate response.

Treatment approach

Replacement (treating established deficiency)

For confirmed deficiency, replacement involves higher doses over a defined period (typically 6–12 weeks) to restore levels, followed by a maintenance dose. Specific doses and durations are discussed in consultation based on your level and individual factors.

Maintenance (preventing recurrence)

After replacement, ongoing daily or weekly supplementation maintains levels. Doses are individualised — people respond differently to the same dose due to body weight, absorption, sun exposure, and genetics.

Form of vitamin D

Vitamin D3 (cholecalciferol) is the form usually used — effective by mouth, well tolerated. Vitamin D2 (ergocalciferol) is also used in some preparations.

Co-factors

Vitamin D works alongside other nutrients (magnesium, vitamin K2). For some patients we discuss combined approaches. Calcium supplementation is sometimes added (but isn’t routinely recommended for everyone — intake from diet is preferable where possible).

Sun exposure

The natural source. UK April-September midday sun for 10–30 minutes on arms and face (skin type-dependent) can produce significant vitamin D. Sun exposure recommendations have to balance vitamin D production against skin cancer risk — not getting sunburnt is the priority. Sun exposure alone usually isn’t enough at UK latitude.

Maintenance and prevention

For UK adults, current guidance recommends maintenance supplementation, particularly in autumn and winter:

• NICE/Public Health England recommends 10 micrograms (400 IU) daily for everyone over 1 year of age in autumn and winter
• Year-round for groups at higher risk (above)
• Higher maintenance doses may be appropriate based on individual response

Dietary sources contribute modestly:

• Oily fish (salmon, mackerel, sardines)
• Egg yolks
• Fortified foods (some cereals, plant milks)
• Mushrooms exposed to UV

Even excellent dietary intake won’t meet vitamin D needs at UK latitude without supplementation or substantial sun exposure.

When to see us

Consider booking if:

• You have symptoms suggestive of deficiency (fatigue, muscle pain, low mood)
• You have risk factors and want to know your baseline level
• You’ve been told you’re "low" but want clear guidance on treatment
• You’ve been taking supplements for a while and want to check it’s working
• You’re pregnant or planning pregnancy
• You have a condition associated with deficiency (autoimmune, osteoporosis, malabsorption)
• You have a child whose vitamin D status you’re concerned about
• You’re considering high-dose supplementation and want clinical guidance

Frequently asked questions

Can’t I just take supplements without testing?

For maintenance doses (around 10 mcg / 400 IU daily), most people can take this without testing first — it’s safe and unlikely to cause toxicity. For higher doses, treating actual deficiency, or assessing response — testing is sensible.

How much does the test cost?

Current prices are on our Fees page. Testing alone is relatively inexpensive.

Can I take too much vitamin D?

Yes — sustained high doses (over 4000–10,000 IU daily for prolonged periods) can cause toxicity (high calcium, kidney problems). This is rare with standard doses and is more likely with unsupervised mega-dosing. We monitor levels in patients on higher doses.

How long does treatment take to work?

Levels rise within weeks of starting supplementation. Symptoms (where attributable to deficiency) often improve over 1–3 months. Stop expecting to feel different overnight.

What about vitamin D drops/sprays?

Various delivery forms exist (tablets, sprays, drops). Generally similarly effective; choose what suits you. Sprays may have slight bioavailability advantage but evidence is mixed.

Do I need vitamin K2 alongside?

Vitamin K2 (MK-7) helps direct calcium to bones rather than soft tissues. For people on high-dose vitamin D long-term, combined K2 is reasonable. For standard maintenance, less critical.

What about magnesium?

Magnesium is required for vitamin D activation. If magnesium is depleted, vitamin D doesn’t work as well. Adequate magnesium intake (through diet primarily) is sensible alongside vitamin D supplementation.

I’m pregnant — should I supplement?

Yes — current NHS guidance recommends vitamin D supplementation throughout pregnancy. We can advise on doses.

My child’s level is low — do they need treatment?

Most likely yes. Children’s requirements and doses differ from adults. We see children for vitamin D assessment.