Osteomalacia and vitamin D deficiency

Definition and distinction. Osteomalacia is defective mineralisation of newly formed osteoid in the mature skeleton, most often due to vitamin D deficiency; the childhood equivalent is rickets. Contrast with osteoporosis, in which mineralisation is normal but bone quantity is reduced. The two commonly coexist in older adults.

Vitamin D falls with ageing. Longitudinal data show vitamin D declines with age, and deficiency is associated with increased mortality. Old skin exposed to ultraviolet light is less effective than young skin at manufacturing cholecalciferol, so sun exposure alone corrects deficiency less reliably in the elderly.

Causes in older adults. Reduced sun exposure — housebound, institutionalised, fully covered clothing, urban living, skin pigmentation (all highly relevant in India); poor dietary intake; malabsorption — coeliac disease, post-gastrectomy, bariatric surgery, pancreatic insufficiency; chronic kidney disease with reduced 1α-hydroxylation; liver disease; and drugs — anticonvulsants, rifampicin, glucocorticoids. Non-vitamin-D causes include hypophosphataemia, renal tubular acidosis and tumour-induced osteomalacia.

Clinical features. Diffuse bone pain and bony tenderness — pelvis, ribs, spine; proximal myopathy with a waddling gait and difficulty rising from a chair; falls; and fragility fractures. In older people this is routinely misdiagnosed as "just ageing", fibromyalgia, polymyalgia rheumatica or metastatic bone disease.

The key biochemical clue. Vitamin D deficiency should be suspected in any older person with a borderline low calcium level and an elevated alkaline phosphatase. The full biochemical picture is: calcium low or low-normal (<8.5 mg/dL), phosphate low, alkaline phosphatase raised, PTH raised (secondary hyperparathyroidism), and 25(OH)D low.

Thresholds. Deficiency <20 ng/mL, insufficiency 20–30 ng/mL, sufficiency ≥30 ng/mL. The textbook position is that ideally vitamin D levels should be 30 ng/mL or greater, matching the International Osteoporosis Foundation target, whereas the Institute of Medicine suggests 20 ng/mL; the threshold concentration associated with clinically relevant disease events is near 20 ng/mL.

Radiology. Generalised osteopenia with blurred, indistinct trabeculae; Looser's zones (pseudofractures) — radiolucent bands perpendicular to the cortex at the medial femoral neck, pubic rami, scapula and ribs; "codfish" biconcave vertebrae; and, in severe disease, a triradiate pelvis. Bone biopsy with tetracycline double labelling is the gold standard but is rarely needed in practice.

Why vitamin D matters beyond bone. In bone, vitamin D stimulates bone turnover while protecting osteoblasts from apoptosis; in muscle it maintains the function of type II fibres, preserving strength and preventing falls. In the Cardiovascular Health Study, vitamin D deficiency was associated with poorer physical performance, lower muscle strength and prevalent mobility and ADL disability. Both osteoporosis and sarcopenia have been linked to the development of frailty.

Treatment. Replete with cholecalciferol: a loading phase — the common Indian regimen is 60,000 IU weekly for 6–8 weeks — followed by maintenance of 800–2000 IU daily, together with elemental calcium 1000–1200 mg/day and adequate dietary protein. Recheck calcium, phosphate, alkaline phosphatase and 25(OH)D at about 3 months; alkaline phosphatase falls last, as healing completes. Always correct vitamin D deficiency BEFORE starting a bisphosphonate or denosumab, or severe hypocalcaemia may follow.

Evidence for benefit and dosing. There is clear evidence that vitamin D 800 IU together with calcium decreases the rate of hip fracture in older people, and this is associated with a decline in mortality. Vitamin D replacement in people who have clear vitamin D deficiency improves muscle strength and decreases falls. Older people should get regular skin exposure of 15–30 minutes per day without sunblock, or take 800–1000 IU of vitamin D per day — this is especially true for residents of long-term care facilities, who require at least 800 IU per day, double the usual recommended daily requirement. Parameter Osteomalacia Osteoporosis Primary hyperparathyroidism Serum calcium Low or low-normal Normal High Serum phosphate Low Normal Low Alkaline phosphatase Raised Normal Raised PTH Raised (secondary) Normal Raised (primary)

Endocrine Society 2024 guideline "Vitamin D for the Prevention of Disease" — a major change in the testing paradigm. The panel suggests empiric daily vitamin D supplementation for everyone aged 75 years and older, because of its potential to lower mortality, and suggests AGAINST empiric supplementation above the dietary reference intake in healthy adults younger than 75. It also suggests against routine 25(OH)D testing in all the populations considered, because no clinical trial evidence supports screening and no optimal target level could be defined — a clear departure from the 2011 guideline's 30 ng/mL target. For non-pregnant people over 50 in whom vitamin D is indicated, daily low-dose administration is preferred to intermittent high doses. Critical distinction for the exam: this guideline addresses disease prevention in generally healthy people — it does not apply to the diagnosis or treatment of established osteomalacia, CKD, malabsorption or hypocalcaemia, where measuring 25(OH)D remains essential.

VITAL trial and the Indian public-health position. In VITAL (25,871 participants, cholecalciferol 2000 IU/day), supplementation did not lower the incidence of invasive cancer or cardiovascular events compared with placebo — but only 12.7% of participants had a 25(OH)D below 20 ng/mL, so the results cannot be applied to genuinely deficient people. This is the key to reconciling "vitamin D does nothing" trial headlines with the real benefit seen in deficiency. In India, where vitamin D deficiency is highly prevalent across all age groups, the pragmatic approach endorsed by ICMR-NIN is food fortification plus routine supplementation of at-risk groups — the housebound, institutionalised and older adults — rather than population-wide testing, which is expensive and does not change management.