Four things measurably change with age: the release of vitamin B12 from food, the fraction of calcium your gut takes up, the amount of vitamin D your skin can make from sunlight, and how much protein a single meal needs before it fully stimulates muscle. Zinc absorption falls too, though less than the raw numbers suggest. Almost everything else is absorbed about as well at 75 as at 25. And the biggest of those changes, the B12 one, has a detail that decides what you should actually do: it is the B12 bound to food protein that fails, not the crystalline B12 in a supplement or a fortified food.
First, the correction: age is not a malabsorption syndrome
The popular version of this topic says that after 50 your digestion quietly stops working and you need to compensate with more of everything. The clinical literature says something narrower. A review of intestinal malabsorption in older patients concluded that malabsorption in this group is infrequent, and that the physiological changes attributable to ageing itself are restricted to calcium, and perhaps zinc and magnesium. What does cause real absorption problems is a list of identifiable conditions that simply become more common with age: atrophic gastritis, small intestinal bacterial overgrowth, pancreatic insufficiency, coeliac disease, and long term medication.
That distinction matters more than it sounds. Ageing is not treatable. Atrophic gastritis, a bacterial overgrowth or a medication effect can be identified and managed. Writing off a low blood value as "just getting older" is how a treatable cause goes unexamined for years. The specialist review of cobalamin and ageing makes the same point in one sentence: diminished absorption should not be viewed as a natural consequence of ageing.
Vitamin B12: the one large, well documented change
B12 is the clearest case, and the numbers are consistent across decades and countries.
In 359 people aged 60 to 99, a pepsinogen I to pepsinogen II ratio below 2.9, the marker of atrophic gastritis of the acid producing stomach lining, was found in 31.5%, and the prevalence rose significantly with age. Within that group, low serum B12, elevated gastrin and anaemia all became more common as the gastritis got more severe.
A clinical review put deficiency at above 20% of elderly people, and attributed more than 60% of those cases to food cobalamin malabsorption, with classic pernicious anaemia responsible for only 15% to 20%. In a Finnish population study of 1,048 people aged 65 to 100, 9.5% met a laboratory definition of deficiency, 6.1% had a total B12 below 150 pmol/l, and a further 32% sat in the borderline 150 to 250 pmol/l band. Being 75 or older roughly doubled the odds. The authors could not find a risk group narrow enough to screen selectively, which is a polite way of saying that you cannot tell by looking.
Why food B12 fails and supplement B12 does not
B12 in food arrives bound to protein. Stomach acid and pepsin have to cut it loose before intrinsic factor can pick it up further down. Atrophic gastritis takes out the acid and pepsin step, so the vitamin stays stuck to the food protein and passes through. Intrinsic factor, further along the chain, is usually still working. That is the mechanism behind the phrase food cobalamin malabsorption.
The crystalline B12 in a supplement or a fortified food is not attached to any protein, so it skips the step that has failed. This is why oral B12 works in exactly the group whose stomachs no longer liberate it from a meal: a review of three randomised trials, a Cochrane review and five prospective cohorts found oral cobalamin adequate to correct deficiency, including in food cobalamin malabsorption. It is one of the rare cases where the supplement form solves a specific mechanical problem rather than topping up a diet.
Our Bioactive Vitamin B-Complex delivers all eight B vitamins in their active coenzyme forms, with B12 as methylcobalamin, which is crystalline and therefore not subject to the food release step. Vitamin B12 contributes to normal red blood cell formation, and the B vitamins contribute to normal energy yielding metabolism and to the reduction of tiredness and fatigue. If you want the difference between the B12 forms themselves, we wrote that up separately in methylcobalamin versus cyanocobalamin.
Often it is the medication, not the birthday
Two of the most common long term prescriptions in older adults interfere with B12, and both effects are quantified.
In a case control study of 25,956 people with a new diagnosis of B12 deficiency compared with 184,199 without, two or more years of proton pump inhibitors carried an odds ratio of 1.65, and two or more years of H2 blockers 1.25. Higher doses tracked with higher odds, 1.95 above 1.5 pills per day versus 1.63 below 0.75. That is observational, so confounding is possible, but the dose response makes chance a weaker explanation.
Metformin has a randomised answer. In 390 people with type 2 diabetes on insulin, 850 mg of metformin three times a day for 4.3 years lowered B12 by 19% against placebo, and raised the absolute risk of deficiency by 7.2 percentage points, a number needed to harm of about 14 people over those 4.3 years. The trial authors recommended regular B12 measurement during long term metformin treatment.
Neither finding is a reason to stop a prescribed medicine. It is a reason to have the level checked, which is a conversation with your doctor and not something a supplement label can decide for you.
Calcium: a genuine, measurable decline
The best dataset here comes from 526 absorption studies in 189 women, studied repeatedly over 17 years under inpatient metabolic conditions. Two things fell out of it. Absorption efficiency drops by roughly 0.0021 per year of age, and there is a separate one time fall of about 0.022 at the loss of oestrogen at menopause.
Do the arithmetic and the honest picture appears. Between 30 and 70 that is 40 years at 0.0021, so about 0.084, plus the 0.022 menopause step: a fall of roughly 0.10 in the fraction of calcium absorbed. In the same dataset, the absorption fraction ran from about 0.45 at very low intakes near 200 mg per day down to about 0.15 above 2,000 mg per day, because the gut compensates when intake is low. A drop of 0.10 against fractions in that range is a meaningful slice, not a rounding error. Two honesty notes: the study was in middle aged women, so stretching the regression to age 80 is my extrapolation rather than their finding, and the range of absorptive performance between individuals was very broad at every intake level.
The mechanism is not settled. When calcium absorption was compared in 59 women aged 25 to 35 and 41 women aged 65 to 83, absorption was lower in the older group, but neither serum 1,25 dihydroxyvitamin D nor the concentration of the intestinal vitamin D receptor differed between them. The authors concluded that the decline cannot be explained by receptor loss and that other factors, not yet understood, are responsible.
We do not sell calcium, and this is not a nudge to buy a calcium supplement. Dietary calcium plus adequate vitamin D status is the standard approach, and higher calcium intakes are absorbed less efficiently anyway.
Vitamin D: the change is in the skin, not the gut
Older skin absorbs dietary vitamin D fine. What falls is production. Skin samples spanning ages 8 to 92 showed an age dependent decrease in epidermal 7-dehydrocholesterol, the precursor the ultraviolet reaction works on, and irradiated samples from two subjects aged 77 and 82 produced more than twofold less previtamin D3 than samples from subjects aged 8 and 18.
Apply the checklist from our piece on judging a study and you will notice the irradiation comparison rests on a handful of skin samples, not a population. It is still the mechanistic anchor everyone cites, and it lines up with the obvious behavioural fact the authors flag: older people who depend on sunlight often expose only a small area of skin, and not often. Combine less precursor with less exposure and less time outdoors and you get a supply problem, in a country where winter sunlight is already too weak to make any, which we covered in how much vitamin D you need in summer versus winter.
Our Vitamin D3 + K2 Drops hold 5000 IU (125 ug) of D3 with 120 ug of vitamin K2 as MK-7 in an MCT oil base, taken as 0.25 ml every three days, not daily. Vitamin D contributes to the normal absorption and utilisation of calcium, to the maintenance of normal bones and to the normal function of the immune system, and vitamin K contributes to the maintenance of normal bones. At this strength, do not exceed the stated intake, and if you take anticoagulants, vitamin K is a question for your doctor before you start.
Zinc: smaller than the headline number
In a 12 week metabolic ward study using stable isotopes, zinc absorption averaged 17% in older men against 31% in young men on the same 15 mg per day diet. Read only that sentence and zinc looks like a crisis. Read the rest and it softens: zinc balance did not differ between the groups, and endogenous zinc losses were lower in the older men. The authors offered two readings, that the lower absorption reflects a lower requirement for absorbed zinc, or that less efficient absorption itself reduces losses. Six men per group, so this is a mechanism study, not a population estimate.
Our Zinc Picolinate Capsules supply 30 mg of elemental zinc per capsule. Zinc contributes to the normal function of the immune system, to normal DNA synthesis and to the protection of cells from oxidative stress. Zinc also competes with copper for uptake, so a high dose taken indefinitely is worth discussing with a clinician rather than adopting by default.
Protein: not absorption, a higher threshold
Protein is the one people get wrong in both directions. Older adults digest and absorb protein. What changes is how much a single meal needs to contain before muscle responds fully.
Pooled dose response data in healthy men found that muscle protein synthesis reached its plateau at about 0.40 g per kg of body mass per meal in men around 71, against about 0.24 g per kg in men around 22. For an 80 kg person that is roughly 32 g in a sitting versus 19 g. The confidence interval on the older figure was wide, plus or minus 0.19, and the analysis was retrospective across several studies, so treat it as a direction rather than a prescription.
The gut is not the bottleneck. When young and older volunteers drank an amino acid mixture, the older group extracted significantly more of it on first pass through the splanchnic tissues, yet muscle protein synthesis and net balance rose just as much as in the young group. More is skimmed off in transit, and the muscle still responds when the meal is large enough.
We do not sell protein powder, and the sensible answer here is food: a real portion of protein at each main meal rather than most of the day's protein at dinner.
What changes less than people claim
Stomach acid and minerals. The line that low stomach acid ruins mineral absorption is repeated everywhere, including in an older article on this blog, and it is not well supported for minerals. When healthy adults were given omeprazole until fasting gastric pH went from 1.8 to 5.8, net absorption of calcium, phosphorus, magnesium and zinc from a standard meal did not change. Thirteen people and short term dosing, so it does not settle long term use, and it does not contradict the B12 findings at all, because B12 depends on acid and pepsin to be cut free from protein while these minerals do not. We are correcting our own older wording rather than defending it.
Iron. Iron deficiency is common in older adults, but a review of 138 papers on iron status in this group frames it the way a clinician would: deficiency and anaemia in an older person are often indicative of underlying disease and should be investigated, and even the cut offs for diagnosing it in older men and women are not agreed. Blood loss, inflammation and kidney function drive far more of it than absorption efficiency does. After menopause, iron requirements fall rather than rise. Iron is the clearest example of a nutrient where the correct response to a low number is a doctor, not a purchase, which is why we do not sell it.
Most water soluble vitamins. Outside B12, the evidence for a general age related fall in absorption is thin. Where older people come up short, the usual driver is eating less overall, not extracting less from what they eat.
What to actually do with this
- Treat B12 as the priority, and measure it. Total B12 alone is a blunt instrument; the Finnish study needed holotranscobalamin and homocysteine to classify the borderline band, and roughly a third of participants sat in that band. Ask your doctor what to test.
- If you take a proton pump inhibitor or metformin long term, have B12 checked periodically. That is the trial authors' own recommendation, not ours.
- Choose crystalline B12. A supplement or fortified food bypasses the release step that fails. This is the one place where the form genuinely fixes the mechanism.
- Spread protein across meals rather than loading dinner, and make each main meal a real portion.
- Keep vitamin D status covered through winter, since the skin route is weaker at both ends, less precursor and less exposure.
- Do not buy calcium or iron on the basis of an article. Both are answered by a blood test and a diet review, and iron in particular can point to something that needs investigating.
Frequently Asked Questions
Do you really absorb less of everything as you get older?
No. The changes attributable to ageing itself are narrow: calcium, and perhaps zinc and magnesium, plus vitamin B12 when atrophic gastritis is present. Most nutrients are absorbed at a similar efficiency across adult life. Where older people fall short, lower total food intake and specific medical conditions explain more than absorption does.
Why can older people absorb B12 from a supplement but not from food?
B12 in food is bound to protein and needs stomach acid and pepsin to be released. Atrophic gastritis removes that step. The B12 in supplements and fortified foods is crystalline and unbound, so it does not depend on that step and is still taken up.
Does taking a proton pump inhibitor mean I will become B12 deficient?
Not necessarily. Two or more years of use was associated with an odds ratio of 1.65 for deficiency in a large case control study, higher at higher doses. That is an increased risk in a population, not a certainty for you, and it is a reason to have the level checked rather than to stop a prescribed medicine on your own.
Should everyone over 50 take a B12 supplement?
Not automatically. Deficiency prevalence in older populations runs above 20% in some clinical reviews, which also means most people are not deficient. Testing tells you which group you are in, and unlike guessing, it costs you one appointment.
Does low stomach acid stop me absorbing minerals?
The direct experiment does not support the blanket version. Raising gastric pH with omeprazole did not change net absorption of calcium, phosphorus, magnesium or zinc from a meal in healthy adults. Acid matters a great deal for freeing B12 from food protein, which is a different mechanism.
Do older adults need more protein per meal?
The dose response evidence points that way: muscle protein synthesis plateaued at about 0.40 g per kg of body mass per meal in older men against about 0.24 g per kg in younger men. The estimate is imprecise and comes from a pooled reanalysis, so use it as a direction, meaning a proper portion at every main meal, rather than a target to the gram.
The Bottom Line
Ageing narrows to a short list: food bound B12, calcium, vitamin D synthesis in skin, a modest fall in zinc absorption, and a higher protein threshold per meal. The single most useful fact on that list is also the most actionable, because the B12 that fails is the B12 attached to food, and the crystalline form in a supplement walks past the broken step. Everything else on the list is answered by a blood test, a conversation about your medication, and a plate with enough protein on it. If you were hoping this article would end with a longer shopping list, it does not, and that is the honest answer.
Sources
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- Carmel R. Cobalamin, the stomach, and aging. The American Journal of Clinical Nutrition, 1997.
- Krasinski SD et al. Fundic atrophic gastritis in an elderly population. Journal of the American Geriatrics Society, 1986.
- Andres E et al. Vitamin B12 (cobalamin) deficiency in elderly patients. CMAJ, 2004.
- Loikas S et al. Vitamin B12 deficiency in the aged: a population-based study. Age and Ageing, 2007.
- Andres E et al. Efficacy of oral cobalamin (vitamin B12) therapy. Expert Opinion on Pharmacotherapy, 2010.
- Lam JR et al. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA, 2013.
- de Jager J et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ, 2010.
- Heaney RP et al. Calcium absorption in women: relationships to calcium intake, estrogen status, and age. Journal of Bone and Mineral Research, 1989.
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- MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. Journal of Clinical Investigation, 1985.
- Turnlund JR et al. Stable isotope studies of zinc absorption and retention in young and elderly men. The Journal of Nutrition, 1986.
- Moore DR et al. Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. The Journals of Gerontology Series A, 2015.
- Volpi E et al. Oral amino acids stimulate muscle protein anabolism in the elderly despite higher first-pass splanchnic extraction. American Journal of Physiology, 1999.
- Serfaty-Lacrosniere C et al. Hypochlorhydria from short-term omeprazole treatment does not inhibit intestinal absorption of calcium, phosphorus, magnesium or zinc from food in humans. Journal of the American College of Nutrition, 1995.
- Wawer AA, Jennings A, Fairweather-Tait SJ. Iron status in the elderly: a review of recent evidence. Mechanisms of Ageing and Development, 2018.
- Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. EUR-Lex, 2012.
This article is general information about nutrition and physiology. It is not medical advice, and it does not diagnose or treat any condition. If you take long term medication or suspect a deficiency, speak to your doctor.
