Bone Health and Osteoporosis: The Nutrition Guide for Women Over 40

Approximately 99 per cent of the body's calcium is stored in bones and teeth, where it provides structural strength. The remaining one per cent circulates in blood and is essential for muscle function, nerve signalling, and blood clotting. When dietary calcium is insufficient, the body resorbs calcium from bone to maintain blood levels — a process that, over time, progressively depletes bone density.

Recommended daily calcium intakes for women rise with age: in the UK, the RNI is 700mg for all adults, but many bone health specialists and organisations including the National Osteoporosis Society recommend 1,000–1,200mg for post-menopausal women and those at risk. In the US, the recommendation is explicitly 1,200mg for women over 50.

Dairy foods are the most calcium-dense and well-absorbed dietary sources. A 200ml glass of milk provides approximately 240mg; a 150g pot of yoghurt approximately 200–250mg; 40g of cheddar cheese approximately 300mg. However, excellent non-dairy sources exist for those who do not consume dairy: tinned sardines and salmon eaten with their bones (providing approximately 300–350mg per 100g), calcium-set tofu (200–350mg per 100g depending on the setting agent), fortified plant milks (typically 120–240mg per 200ml), kale (150mg per 100g cooked), bok choy (158mg per 100g), broccoli (47mg per 100g), white beans (130mg per 100g), almonds (76mg per 30g), and sesame seeds and tahini.

Calcium absorption efficiency varies considerably by source and context. Calcium from dairy is absorbed at approximately 30–35 per cent. Calcium from some plant sources (kale, bok choy, broccoli) is similarly or slightly more bioavailable. However, calcium from spinach and Swiss chard is poorly absorbed due to high oxalate content — though these are still good overall health foods. Calcium supplements are best taken in doses of no more than 500mg at a time to maximise absorption, and ideally with food and vitamin D.

Vitamin D is essential for calcium absorption in the gut. Without adequate vitamin D, only 10 to 15 per cent of dietary calcium is absorbed; with sufficient vitamin D, this rises to 30 to 40 per cent. This means that even a high-calcium diet is substantially undermined if vitamin D status is poor — a reality reflected in the high prevalence of osteoporosis even in populations with good dairy consumption.

Vitamin D deficiency is remarkably prevalent. In the UK, an estimated 40 per cent of adults are deficient in winter, and 16 per cent year-round. Post-menopausal women, those with darker skin tones, those who cover their skin for cultural or religious reasons, those who are largely housebound, and those living at northern latitudes (above 50°N) are at particularly high risk. In these groups, sun-derived vitamin D production is minimal for much of the year.

The UK NHS advises all adults to consider a daily vitamin D supplement of 10 micrograms (400 IU) from October to March; for those at higher risk of deficiency, year-round supplementation is recommended. Many bone health specialists and endocrinologists recommend higher doses — 1,000 to 2,000 IU daily — to maintain serum 25-hydroxyvitamin D levels above 50 nmol/L, the level associated with optimal calcium absorption and bone mineral density.

Dietary sources of vitamin D are limited: oily fish (salmon, mackerel, herring, sardines) provide 200–400 IU per portion; egg yolks provide approximately 40 IU each; UV-exposed mushrooms can provide meaningful amounts (turning mushrooms gill-side-up in sunlight for 30–60 minutes dramatically increases their vitamin D content); and fortified foods (plant milks, some cereals, orange juice) typically provide 100–200 IU per serving. Given these relatively modest food amounts, supplementation is practical and safe for most adults.

Calcium and vitamin D dominate the bone health conversation, but several other nutrients play crucial roles that are frequently overlooked.

Magnesium is involved in over 300 enzymatic reactions and is essential for bone formation. Approximately 60 per cent of the body's magnesium is stored in bone as part of its crystalline structure. Magnesium stimulates the enzyme alkaline phosphatase, which is involved in bone mineralisation, and helps convert vitamin D to its active form. Low magnesium status is associated with reduced bone mineral density and increased fracture risk. The best dietary sources are dark chocolate (70%+ cocoa), pumpkin seeds, almonds, spinach, cashews, black beans, avocado, and wholegrains. Many people with Western diets are magnesium-insufficient; a supplement of 300–400mg magnesium glycinate or citrate daily is a reasonable option if dietary intake is low.

Vitamin K2 (menaquinone) directs calcium into bones and teeth and away from soft tissues and blood vessels — a property that makes it a valuable complement to calcium and vitamin D supplementation. It activates osteocalcin (a bone matrix protein that binds calcium) and matrix Gla-protein (which inhibits vascular calcification). The best dietary sources of K2 are natto (fermented soy beans, a staple of Japanese diets — notably the population with some of the lowest hip fracture rates globally), fermented cheeses (Gouda, Brie, Edam), and egg yolks. Many bone health supplements now include K2 alongside calcium and vitamin D.

Protein is a component of the bone matrix (collagen provides the scaffolding that calcium minerals are deposited onto) and is essential for bone repair. Higher protein intakes are associated with better bone mineral density in older women, not worse — the old concern that protein increased calcium excretion has been largely refuted by research showing that adequate protein actually enhances calcium retention when calcium intake is sufficient. Aim for 1.2g of protein per kilogram of body weight or above.

Just as important as knowing which nutrients protect bone is understanding which dietary habits actively undermine it.

Excessive alcohol impairs calcium absorption, reduces vitamin D activation, and is directly toxic to osteoblasts (bone-building cells). Women who consume more than two standard drinks per day have significantly lower bone mineral density and higher fracture risk than those who drink less or abstain. Moderate drinking (up to one drink per day) appears to have a neutral to slightly positive effect on bone density, possibly due to alcohol's mild oestrogenic effects, but this is not a reason to start drinking if you do not already.

Heavy caffeine intake — more than four cups of coffee per day — increases urinary calcium excretion and is associated with reduced bone mineral density in women with low calcium intake. At moderate intakes (one to two cups), the effect is minimal and is easily offset by adding a splash of milk to each cup.

Very high sodium intake increases urinary calcium excretion. For every 2,300mg of sodium (approximately one teaspoon of salt) consumed, approximately 40mg of additional calcium is lost through urine. Reducing highly processed foods, which account for the majority of sodium intake, therefore has a secondary benefit for bone health alongside its cardiovascular benefits.

Physical inactivity is perhaps the most powerful non-nutritional driver of bone loss. Weight-bearing exercise — walking, jogging, dancing, tennis, and strength training — provides the mechanical loading signals that stimulate osteoblasts to build bone. Resistance training with weights or resistance bands is particularly effective, with research showing meaningful increases in bone mineral density even in women who begin in their 50s and 60s. Exercise and nutrition work synergistically — neither is sufficient alone.

Putting all of this together into a practical daily eating pattern requires planning but not perfectionism. The following framework provides the nutritional foundation for bone health from the perimenopausal years onwards.

Aim for 1,000–1,200mg of calcium from food daily. A practical approach: two to three servings of dairy or calcium-fortified plant milk, one serving of oily fish with bones (sardines on toast, tinned salmon salad), a serving of white beans in a meal, and a portion of kale or bok choy. Track your intake for a week using a nutrition app to see where you currently stand and where gaps exist.

Supplement vitamin D to maintain adequate blood levels year-round — 1,000 IU daily is a reasonable dose for most adults in northern climates; higher doses may be needed for those with documented deficiency (discuss with your GP). Take it with a meal containing fat for better absorption.

Include magnesium-rich foods daily — a handful of almonds or pumpkin seeds, some dark chocolate, a portion of legumes, or leafy greens contributes meaningfully. Consider a magnesium supplement if dietary intake is consistently low.

Eat protein at every meal — eggs at breakfast, chicken or fish at lunch, legumes or dairy at dinner — to support both bone matrix maintenance and muscle mass preservation (which reduces fall risk, reducing fracture risk further).

Reduce alcohol and caffeine from the extremes; minimise ultra-processed food and excess salt. And use every opportunity to incorporate weight-bearing movement — walking to destinations, taking the stairs, adding a bodyweight circuit to your morning routine.