Vitamin D and Bone Health After 40

Women lose bone faster in the years immediately around their final period than at any other point in life — commonly a few percent per year in the spine during that window. About half of women over 50 will have an osteoporosis-related fracture, and a hip fracture in later life is a genuinely serious event, not an inconvenience.

Vitamin D is where most people start. It is a reasonable place to start. It is not the whole answer, and the way it is usually taken wastes the opportunity.

What vitamin D actually does for bone

Vitamin D's central job is calcium absorption. Without adequate vitamin D, you absorb a fraction of the calcium you eat regardless of how much you eat. It also supports muscle function, which matters more than it sounds — a large share of fractures come from falls, and falls come from weak legs and poor balance.

Note the framing. Vitamin D makes calcium usable. It does not build bone by itself, and supplementing it in someone who is already replete does very little. This is why large trials of vitamin D alone in unselected, mostly-sufficient populations have repeatedly come out neutral for fractures — and why that null result does not mean vitamin D is unimportant. It means topping up a full tank does nothing.

Why deficiency is common anyway, even in sunny countries

Skin synthesis requires UVB, which reaches usable intensity only around midday and is filtered by glass, sunscreen, clothing, and higher latitudes. Meanwhile:

• Darker skin requires substantially longer sun exposure for the same synthesis.
• Indoor work removes the midday window entirely.
• Age reduces the skin's synthetic capacity.
• Higher body fat sequesters vitamin D, lowering circulating levels.
• Very few foods contain it — fatty fish, egg yolk, and fortified products, and that is roughly the list.

Deficiency is common in Latin America despite the latitude, largely for the reasons above. Do not assume sunshine equals sufficiency.

Testing and targets

The relevant blood test is 25-hydroxyvitamin D (25(OH)D).

Widely used interpretation: below 30 nmol/L (12 ng/mL) is deficient and associated with poor bone outcomes; 50 nmol/L (20 ng/mL) is generally considered adequate for bone health in most people. Some clinicians target somewhat higher. There is no good evidence that pushing levels far above the adequate range produces further benefit, and there is evidence that very high levels are harmful.

Testing is worthwhile once if you have risk factors — very little sun exposure, darker skin, malabsorption conditions, obesity, or an existing osteoporosis diagnosis. Routine repeated testing in healthy people is usually unnecessary.

Dosing, plainly

Typical maintenance: 800–2,000 IU of vitamin D3 daily for adults over 50 covers most people. D3 (cholecalciferol) is preferred over D2; it raises and maintains blood levels more effectively.

Take it with the fattiest meal of the day. It is fat-soluble; absorption on an empty stomach is meaningfully worse.

Correcting a documented deficiency may require a higher loading regimen — that should be guided by a clinician and followed by a repeat test, not self-prescribed indefinitely.

The upper limit is 4,000 IU per day for adults without medical supervision. More is not better. Chronic very high intake causes hypercalcemia — nausea, weakness, kidney stones, and kidney damage. The mega-dosing culture around vitamin D is one of the few genuinely risky supplement trends.

Vitamin D alone is not a bone plan

This is the part that gets skipped, and it is the part that matters.

Calcium. Roughly 1,000–1,200 mg a day for women over 50, preferentially from food — dairy, fortified plant milks, sardines with bones, tofu set with calcium, leafy greens. Supplemental calcium at high doses has a less favourable risk profile than dietary calcium; use supplements to close a gap, not to replace food.

Vitamin K2. Plausible mechanism in directing calcium to bone, promising but not definitive evidence. Reasonable to include, not worth agonising over.

Protein. Bone is roughly half protein by volume. Adequate intake is associated with better bone density, not worse.

Loading. This is the biggest lever and the one no capsule replaces. Bone remodels in response to mechanical strain. Resistance training and impact — jumping, hopping, stair climbing where safe — are what actually signal bone to rebuild. Swimming and cycling, for all their virtues, do not.

Not smoking, and limiting alcohol. Both directly reduce bone density.

The practical version

If you are over 45, take 1,000–2,000 IU of D3 with your largest meal, eat calcium rather than swallowing it, lift heavy things twice a week, and ask for a 25(OH)D test at your next bloodwork if you have any risk factor. If you have a family history of osteoporosis or an early menopause, ask about a DEXA scan sooner rather than later — you cannot rebuild what you did not know you were losing.