Vitamin D: Why You Can’t Eat Your Way There — and Who the Pill Actually Helps

A salmon dinner barely covers a day’s vitamin D, and the food list runs out fast. Here is who truly needs the supplement, who got oversold, and why pregnant women top the list.

A patient asked me last month if she could skip the vitamin D pill and just eat better. It is a fair question. Nobody wants another bottle on the counter. So I did the math with her, out loud, and watched her face change.

Here is the problem.

Vitamin D is barely a food vitamin at all. Your body was built to make it in your skin from sunlight, not to pull it off a plate. Very few foods carry a useful amount. The richest is oily fish. A 3.5-ounce piece of wild salmon gives you somewhere around 570 to 650 units. Farmed salmon gives less, often closer to 440. Mackerel runs high, near 640. Canned sardines sit around 190, herring around 170. After that, the list falls off a cliff. An egg yolk has about 40 units. A glass of fortified milk has about 100. Most other foods have almost none.

Now set that against what an adult needs each day: about 600 units under age 70, and 800 after.

To reach that with food alone, you would need oily fish on your plate nearly every single day. Most people eat fish twice a week if they are trying. And the fish itself is unreliable — wild salmon can carry three or four times the vitamin D of farmed, and you rarely know which one is on your fork. So for the average person, food does not get there. That part is not up for debate. It is arithmetic.

Sunlight is the natural answer, and for most of human history it was the only one. But modern life works against it. If you live in the northern half of the country, your skin makes almost no vitamin D from October to March. Sunscreen blocks it, which is the right trade when the other option is skin cancer. Office work blocks it. Darker skin needs more sun to make the same amount. Age cuts production too. So the natural source is real, but for most people it is not enough.

This is where the story gets interesting, because the supplement world ran ahead of the evidence. For years the message was that everyone should take high doses, and that more was always better. Then the large trials arrived. VITAL, a study of more than 25,000 American adults, tested 2,000 units a day against a dummy pill. It did not lower cancer. It did not lower heart attacks or strokes. A companion study found it did not prevent broken bones either. In 2024 the Endocrine Society read all of this and made a quiet, sensible call: most healthy adults under 75 do not need to supplement beyond the basic amount, and most do not even need a blood test to check their level.

That sounds like an argument against the pill. It is not. It is an argument against the hype, and against treating a deficiency drug like a daily ritual for people who are already fine. Because the same trials, read honestly, show exactly who does benefit.

Pregnant women sit at the top of that list, and this is my field. The Endocrine Society recommends vitamin D in pregnancy because it is tied to lower rates of preeclampsia, preterm birth, babies born too small, and newborn death. Those are not small things. Children benefit too — vitamin D prevents rickets and lowers respiratory infections. Adults over 75 have a lower risk of death. And there is one finding that matters especially for women: in VITAL, vitamin D cut the rate of new autoimmune disease by about 22 percent — conditions like rheumatoid arthritis, thyroid disease, and psoriasis. The protection held up over seven years of follow-up, with 156 cases on vitamin D against 198 on placebo. Women develop autoimmune disease far more often than men, so this benefit lands harder for them. Then add the simplest case of all: anyone whose level is genuinely low. In VITAL, about 1 in 8 adults started out deficient, and another third were borderline. Fixing a true deficiency is not hype. It is repletion.

So what do I tell patients now?

Diet will not carry this nutrient for most people. Eat the oily fish and the fortified foods, get safe sun when you can, but do not expect your plate to close the gap. Then match the pill to the person, and to a real number.

For a healthy adult, the baseline target is 600 IU a day up to age 70, and 800 IU after that. If you are pregnant, aim higher: the trials behind the recommendation used 600 to 5,000 IU a day and averaged about 2,500, so a daily supplement of 1,000 to 2,000 IU, on top of the vitamin D already in your prenatal, is a sound and common target.

Children aged 1 to 18 do well on about 1,200 IU a day, and a baby under one needs 400 IU. If your blood level is genuinely low, 1,000 to 2,000 IU a day will usually bring it back up. If you are a healthy 40-year-old man with a normal level, you do not need to chase a higher number, and you should stay under the adult ceiling of 4,000 IU a day, because very high doses carry their own risk of harm.

More is not better here. Enough is better.

One honest caveat, because it cuts the other way. The big no-benefit trials enrolled mostly people who already had enough vitamin D. So no extra benefit may really mean no benefit on top of enough. That is a fair criticism, and it is exactly why I aim at deficiency rather than at the supplement aisle.

My take: this is not a debate about whether vitamin D is essential. It is. The real question is how you get it and who needs help getting it.

Food alone rarely gets anyone to the target.

Sunlight is unreliable in modern life.

And a cheap daily pill closes the gap for the people the evidence actually points to — pregnant women first among them. Replete the deficient, protect the pregnant, and stop megadosing the healthy.

Bottom line: skip the megadose, not the basics. If you are pregnant, older, or low, take the small daily dose — your dinner plate cannot do this job. If this helped you think more clearly about what is on your counter, subscribe to ObGyn Intelligence. The evidence here is better than the marketing, and it stays that way.

References

1. Manson JE, Cook NR, Lee IM, Christen W, Bassuk SS, Mora S, et al. Vitamin D supplements and prevention of cancer and cardiovascular disease. N Engl J Med. 2019;380(1):33-44. doi:10.1056/NEJMoa1809944. PMID 30415629.

2. LeBoff MS, Chou SH, Ratliff KA, Cook NR, Khurana B, Kim E, et al. Supplemental vitamin D and incident fractures in midlife and older adults. N Engl J Med. 2022;387(4):299-309. doi:10.1056/NEJMoa2202106.

3. Hahn J, Cook NR, Alexander EK, Friedman S, Walter J, Bubes V, et al. Vitamin D and marine omega-3 fatty acid supplementation and incident autoimmune disease: VITAL randomized controlled trial. BMJ. 2022;376:e066452. doi:10.1136/bmj-2021-066452. PMID 35082139.

4. Costenbader KH, Cook NR, Lee IM, Hahn J, Walter J, Bubes V, et al. Vitamin D and marine n-3 fatty acids for autoimmune disease prevention: outcomes two years after completion of a double-blind, placebo-controlled trial. Arthritis Rheumatol. 2024;76(6):973-983. doi:10.1002/art.42811. PMID 38272846.

5. Demay MB, Pittas AG, Bikle DD, Diab DL, Kiely ME, Lazaretti-Castro M, et al. Vitamin D for the prevention of disease: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2024;109(8):1907-1947. doi:10.1210/clinem/dgae290.