A Tuesday regular at Seasons of Grace — seventy-six, a retired church organist — pulled a lab printout from her purse last week and slid it across the café table. Her doctor had circled one number in pen: 25(OH)D, 18 ng/mL. Underneath, in the margin, he'd written low — start D3. She wanted to know what it meant. She also wanted to know, quietly, whether this was the reason she'd been struggling to push up out of her low porch chair without a hand on the railing.
I'm not her doctor. I'm a wellness counselor, and the first question was easier than the second. But the two sat together on that table the way most health questions do — a number on a page, and a body that has been quietly asking to be heard.
Vitamin D, in our seventies, is one of those small, unglamorous things that turns out to matter more than the headlines suggest. Not a miracle. But the basic biology of how we make it, hold onto it, and use it really does change with age. It's worth understanding what the numbers mean before we start chasing them.
Why Aging Changes the Vitamin D Conversation
Most of us spent our younger years not thinking about vitamin D at all. The body made it. We walked outside and that was that. After about seventy, three things shift at once.
The skin itself becomes a less efficient factory. By age 70, the same square inch of skin produces roughly half the vitamin D it made at age 20 from the same amount of sunlight (NIH ODS). The starting material — a cholesterol precursor called 7-dehydrocholesterol — simply runs lower in older skin. Then the kidneys, which take vitamin D the rest of the way to its active hormone form (the step called 1-alpha-hydroxylation), become slower at the conversion. Add in the modestly reduced gut absorption that often comes with age, plus the fact that many of us spend less time outside than we used to, and the math turns against us.
This isn't a moral failing. It's physiology. The same body that used to produce all the vitamin D it needed by walking to the mailbox in shorts is now asking for a little more help — from food, from a small daily pill, from honest conversation with a clinician who knows your full picture.
The Numbers Worth Knowing
There is real, ongoing disagreement about how much vitamin D older adults need and what blood level counts as enough. I think it helps to know the disagreement exists rather than pretend it doesn't.
The Institute of Medicine (now the National Academy of Medicine) sets the Recommended Dietary Allowance at 800 IU — that's 20 mcg — per day for adults 71 and older. They consider a serum 25(OH)D level of at least 20 ng/mL sufficient for bone health in the general population. The Endocrine Society, in its clinical practice guidelines, has historically recommended a higher target — ≥30 ng/mL — and often suggests 1,500 to 2,000 IU per day for older adults at risk of deficiency. Their 2024 guideline update softened some of this for healthy adults under 75, but kept a higher-touch approach for adults over 75 and for those who are frail or housebound.
The USPSTF, looking at the same evidence from a population-screening angle, has concluded there isn't enough proof to recommend universal vitamin D screening in community-dwelling adults — but that recommendation explicitly excludes people who are already at risk, which most of us in our seventies and eighties quietly are.
The upper limit is just as worth knowing as the floor. The IOM sets the tolerable upper intake at 4,000 IU per day. Sustained intake above 10,000 IU/day moves into territory where toxicity — high blood calcium, kidney stones, kidney damage — becomes a real risk. More is not better past a certain point. It's just more.
If I had to translate all of that into something I could say to my Tuesday regular at the café: most older adults do well at 800 to 2,000 IU of D3 per day, with a blood level somewhere between 30 and 50 ng/mL, retested after about three months of supplementation to see where you've landed. The number to discuss with your clinician isn't a brand or a megadose. It's the dose that fits your labs, your meds, and your life.
Food First, Honestly
Food alone rarely gets older adults to a sufficient blood level — there just aren't that many vitamin D-rich foods, and we don't tend to eat them in big quantities. But food matters, and the numbers are easier to plan with than people realize.
A few real portions, per NIH ODS:
- 3.5 ounces of cooked salmon: roughly 570 IU
- 3 ounces of canned albacore tuna in oil: about 230 IU
- 1 cup of fortified milk: roughly 100 IU
- 1 cup of fortified orange juice: about 100 IU
- One large egg yolk: around 40 IU
- 3 ounces of fortified cereal with milk: 150 to 200 IU, depending on brand
A Saturday breakfast of two scrambled eggs, a glass of fortified orange juice, and a bowl of fortified cereal with milk lands you somewhere around 380–440 IU before you've left the table. A salmon dinner that night gets you well past the daily RDA. Most days won't look like that, which is exactly the point — food sets the foundation. A modest supplement, taken with the meal that has the most fat in it (vitamin D is fat-soluble — absorption climbs measurably when it rides along with food that contains some oil or butter), usually closes the gap.
While we're talking about food, our healthy eating guide walks through what a real, joyful week of senior nutrition can look like — not a diet plan, just a steadier relationship with the kitchen.
Sun, Honestly
The sun is still our oldest source. It's also the one most often misrepresented.
A few honest things to hold together:
- Above roughly 37° north latitude — a line that runs through Richmond, San Francisco, and Wichita — the sun sits too low in the sky from late fall through early spring to make meaningful vitamin D, no matter how long you stand outside. UVB simply doesn't reach the skin at the right angle.
- Skin tone changes the timing. More melanin in the skin is a gift in many ways, but it lengthens the time needed under direct sun to produce the same amount of vitamin D. Someone with darker skin may need three to five times longer in the same sun than someone with very fair skin to make the same dose.
- Sunscreen blocks synthesis — and that is not a reason to skip sunscreen. Skin cancer is real, and it is worse the older we get. The trade-off is not sunscreen versus vitamin D. It's sunscreen plus food plus, where needed, a small supplement.
- Older skin makes less per minute of sun than younger skin, even at the same latitude on the same day.
Fifteen minutes on the porch with your forearms in the morning sun is a lovely thing. I do it most mornings myself, weather allowing. But I don't kid myself that it's a treatment plan in February in the Blue Ridge. It isn't.
Supplements: D3, D2, and the Quiet Details
If supplementation is on the table, a few practical pieces are worth knowing.
D3 (cholecalciferol) raises blood levels more efficiently than D2 (ergocalciferol) for most people. Most over-the-counter senior multivitamins and standalone D supplements are now D3. D2 still has a role — it's the prescription form often used for short, high-dose correction of severe deficiency — but for daily maintenance, D3 is the workhorse.
A few details that matter more than the brand:
- Take it with a meal that has some fat — eggs, avocado, olive oil on toast, a piece of cheese. Absorption climbs noticeably.
- Daily versus weekly dosing: For most people, a small daily dose tracks more steadily with how the body actually uses vitamin D. Larger weekly or monthly doses have shown mixed results in older adults — some studies have linked very large monthly bolus doses to more falls in seniors, which is exactly what we don't want.
- Interactions worth flagging to your clinician: thiazide diuretics (which raise blood calcium and can interact with high-dose D), some seizure medications (which speed up vitamin D metabolism), corticosteroids, and conditions involving fat malabsorption — celiac, Crohn's, after certain bariatric surgeries. Sarcoidosis is a specific contraindication for high-dose vitamin D; the inflamed tissue itself can over-activate the vitamin and push blood calcium dangerously high. The AGS Beers Criteria, which guides safer prescribing in older adults, doesn't ban vitamin D — but it does flag the broader principle of being cautious with anything that nudges calcium upward in someone already on multiple medications.
None of this means a senior shouldn't take vitamin D. It means the conversation belongs with a clinician who knows your full medication list, not the supplement aisle at Costco.
What Deficiency Actually Feels Like
This is the part most articles miss, and it's the part my Tuesday regular was really asking about.
The textbook signs of severe deficiency — bone pain, the soft-bone disease called osteomalacia — are real but usually late. The earlier signs in older adults are quieter and easy to mistake for just getting older:
- Proximal muscle weakness: trouble standing up from a low chair without using your hands; tired thighs going up the porch steps; a sense that the legs aren't quite under you.
- Vague, diffuse aches — not sharp joint pain, more a low hum of soreness.
- Increased falls or near-falls. Vitamin D matters for muscle function, not just bone, and the falls connection is one of the more consistent threads in the research. Some of what we do at Seasons of Grace around fall prevention — leg strength, balance, the unglamorous repetition of standing and sitting — works alongside, not instead of, getting D levels into a reasonable range.
- A low, flat mood. Not clinical depression on its own, but a kind of dimming. Worth mentioning to your clinician, not as the cause but as one piece of the picture.
These signs aren't proof of deficiency. They're a reason to ask for a 25(OH)D test — especially if you live north of that 37th parallel, spend most of your time indoors, take medications that affect bone metabolism, or are recovering from a fracture or fall. A retest about three months after starting a supplement tells you whether the dose is doing what it's supposed to.
What Vitamin D Does Not Do
This matters, because the supplement aisle has a way of overpromising.
The VITAL trial, published in the New England Journal of Medicine in 2019 with follow-up reports continuing into the 2020s, gave roughly 25,000 older U.S. adults either 2,000 IU of vitamin D3 daily or a placebo and watched what happened over five years. The headline finding: in adults who started out at reasonable vitamin D levels, supplementation did not reduce overall cardiovascular events, did not reduce overall cancer incidence, and did not significantly reduce fractures in the general study population.
Later analyses have nuanced that picture — there's a signal that vitamin D may modestly reduce advanced cancer and cancer mortality in some subgroups, and the bone and falls picture appears more meaningful in adults who were genuinely deficient at baseline than in those already replete. But the broad lesson stands: more vitamin D doesn't buy more health once your tank is full. The benefit is in correcting deficiency, not topping off.
That's a useful frame for any conversation with your doctor. Not should I take more, but am I where I should be, and if not, what's the smallest dose that gets me there.
A Small Practice for Tomorrow
My Tuesday regular went home that afternoon with a plan that fit on a 3x5 card: ask her doctor for a target blood level she could write down, start the D3 he'd recommended with her morning eggs, walk fifteen minutes on her front sidewalk in the late-morning sun when the weather allowed, and come back in three months for a retest.
That's most of it, really. A number on a page, a small daily habit, a clinician who knows the whole of you, and the willingness to keep asking — gently, persistently — what your body is trying to say.
We are not meant to figure all of this out alone. Ask the question. Get the test. Take the small dose with the eggs. And tomorrow morning, if the weather is good and the porch is dry, sit outside for a few minutes with your sleeves pushed up — not as a treatment plan, just as a way of remembering that the sun is still part of how we belong to the world.
