Just EnoughVitamin D and calcium are often spoken about together, for good reason.
Calcium provides mineral for your skeleton. Vitamin D helps your body absorb calcium and plays an important role in maintaining healthy bones.
But vitamin D presents an unusual problem: it’s difficult to know exactly how much you’re getting.
Where does vitamin D come from?
There are three main sources.
Sunlight. Your skin can make vitamin D when exposed to ultraviolet B radiation.
Food. Vitamin D occurs naturally in a relatively small number of foods, and is added to some fortified foods.
Supplements. Vitamin D is available on its own, and appears in many multivitamins and bone-health supplements.
That last point matters. You may be taking more vitamin D than you realise, because the same nutrient can appear in several products.
Sunlight isn’t a dose
You can’t look at 20 minutes outdoors and translate it neatly into a particular number of international units.
Vitamin D production from sunlight varies with latitude, season, time of day, skin pigmentation, clothing and how much skin is exposed.
That makes time outdoors useful information to track, but not a precise vitamin D dose.
It also means vitamin D advice shouldn’t quietly become advice to expose yourself excessively to UV radiation.
What happens after 40?
Bone is living tissue. Throughout life, old bone is broken down and replaced.
With ageing — and particularly around and after menopause — the balance can shift towards greater bone loss.
Vitamin D is one part of the picture. So are calcium, adequate protein, resistance and weight-bearing exercise, hormones, medicines, smoking, alcohol and other health factors.
There isn’t one nutrient that can carry the entire job.
More vitamin D isn’t automatically better
Vitamin D is fat-soluble, which means excessive supplemental intake can accumulate.
Very high vitamin D intake can cause excessive calcium levels in the blood and urine, potentially leading to problems including kidney stones and kidney damage.
This is why vitamin D has an upper intake limit as well as a recommended intake.
An upper limit isn’t the amount to aim for. It’s a boundary intended to help reduce the risk of harm.
There are circumstances in which clinicians prescribe doses above ordinary nutritional recommendations to treat diagnosed deficiency. That is different from routinely taking high-dose vitamin D yourself.
Check everything you’re taking
Imagine taking:
- a vitamin D supplement;
- a calcium-and-vitamin-D tablet; and
- a multivitamin containing vitamin D.
Each dose may look unremarkable on its own.
Together, they’re your actual supplemental intake.
Calcium depends on vitamin D to be absorbed at all — which is why counting one without the other gives an answer you cannot rely on. The same principle applies to calcium. This is why reading the whole label matters more than reading the product name — and why combination products can hide the real total.
Vitamin D isn’t a substitute for loading your bones
Vitamin D and exercise work differently.
Vitamin D helps maintain the biological conditions necessary for healthy bones. Exercise provides a physical stimulus.
Research examining exercise and vitamin D together reinforces the broader point: bone health is not the product of one pill or one behaviour.
The Just Enough principle
Count what you take.
Know what you’re aiming for.
Know the upper limit too.
And remember that supplements are only one part of keeping bones strong.
Evidence
The Just Enough evidence library includes Rizzoli et al. (2024), a current review covering calcium, vitamin D, protein and dietary patterns, and Fischer et al. (2023), a systematic review and meta-analysis examining vitamin D supplementation alongside exercise and bone mineral density.
The broader clinical evidence base used by Just Enough includes current UK, US and Canadian osteoporosis guidance covering nutrition, exercise, assessment and fracture prevention.
Just Enough provides general information, not medical advice. Vitamin D requirements and appropriate supplementation can differ according to individual circumstances. A healthcare professional can assess suspected deficiency and advise on treatment.