Vitamin D, B12 and folate supplementation

Why these three matter

Each of Vitamin D, Vitamin B12 and folate has a direct role in nervous system function. Severe deficiency can cause measurable cognitive impairment that improves with replacement. UK memory clinics test all three as standard.

Vitamin D

Vitamin D insufficiency is common in the UK because of limited sun exposure between October and March. Cognitive effects of severe Vitamin D deficiency are less well established than for B12, but observational evidence links low Vitamin D with cognitive decline.

Targets

• Sufficient: 25-OH Vitamin D above 50 nmol/L;
• Insufficient: 25 to 50 nmol/L;
• Deficient: under 25 nmol/L.

NHS guidance

Consider a daily 10 microgram (400 IU) supplement between October and March for the whole UK population, and year-round for those with limited sun exposure (older adults, housebound, dark skin tones). Higher doses (1,000 to 4,000 IU daily) for confirmed deficiency under medical advice.

Vitamin B12

B12 deficiency is a well-recognised reversible cause of cognitive impairment. Cognitive symptoms can include memory loss, slowed thinking and personality change. Other features include peripheral neuropathy, anaemia and glossitis. Causes include:

• Reduced absorption in older adults (autoimmune gastritis, atrophic gastritis);
• Vegetarian and vegan diets without supplementation;
• Long-term Metformin or proton pump inhibitor use;
• Crohn's disease, coeliac disease, gastric surgery;
• Pernicious anaemia.

Treatment

• Intramuscular B12 injections (hydroxocobalamin 1 mg every 2 to 3 months) for established deficiency, with loading doses initially;
• High-dose oral B12 (1,000 to 2,000 micrograms daily) for some causes;
• Cognitive symptoms usually improve over weeks to months;
• Severe long-standing deficiency may not fully reverse.

Folate

Folate deficiency similarly affects cognition. Causes include poor diet, alcohol, certain medications (Methotrexate, Phenytoin) and malabsorption. Treatment is with oral folic acid (5 mg daily) for several months, with attention to the cause.

Folate replacement should not be started before B12 deficiency has been excluded or corrected, because folate alone in the presence of B12 deficiency can worsen neurological symptoms.

The wider picture: supplements for dementia prevention

Beyond correcting confirmed deficiency, the evidence for routine supplements in dementia prevention is weak:

• Multivitamins: large trials (COSMOS, PREADViSE) have shown mixed results; some signal of benefit;
• Omega-3 fatty acids: oily fish in the diet preferable to supplements;
• Vitamin E: not recommended;
• Ginkgo biloba: no consistent benefit;
• Curcumin: early-phase research only.

Eating well usually serves you better than supplementation alone.

When to test

Memory clinic blood panels include B12, folate, Vitamin D, thyroid function, full blood count, kidney function, lipid profile and HbA1c. Annual checking is appropriate for many older adults, particularly those on Metformin or proton pump inhibitors, vegetarians and vegans, or with chronic illness.