Vitamin D Table
| Age | RDA mcg | RDA IU | Upper limit IU |
|---|---|---|---|
| 0-6 months | 10* | 400* | 1,000 |
| 7-12 months | 10* | 400* | 1,500 |
| 1-3 years | 15 | 600 | 2,500 |
| 4-8 years | 15 | 600 | 3,000 |
| 9-13 years | 15 | 600 | 4,000 |
| 14-18 years | 15 | 600 | 4,000 |
| 19-50 years | 15 | 600 | 4,000 |
| 51-70 years | 15 | 600 | 4,000 |
| Over 70 | 20 | 800 | 4,000 |
| Food | Serving | mcg | IU | %DV |
|---|---|---|---|---|
| Cod liver oil | 1 tbsp | 34.0 | 1,360 | 170% |
| Trout, rainbow, farmed, cooked | 3 oz | 16.2 | 645 | 81% |
| Salmon, sockeye, cooked | 3 oz | 14.2 | 570 | 71% |
| White mushrooms, UV-exposed | 1/2 cup | 9.2 | 366 | 46% |
| Milk, 2%, fortified | 1 cup | 2.9 | 120 | 15% |
| Soy/almond/oat milk, fortified | 1 cup | 2.5-3.6 | 100-144 | 13-18% |
| Ready-to-eat cereal, fortified | 1 serving | 2.0 | 80 | 10% |
| Egg | 1 large | 1.1 | 44 | 6% |
| Serum 25(OH)D nmol/L | ng/mL | What it means |
|---|---|---|
| <30 | <12 | Deficiency - rickets in children, osteomalacia in adults |
| 30 to <50 | 12 to <20 | Inadequate for bone and overall health in many people |
| 50 to 125 | 20 to 50 | Generally adequate |
| >125 | >50 | High - potential adverse effects above this band |
The vitamin D table hangs on one number most supplement labels never say out loud: for virtually everyone from age 1 through 70, the NIH recommended dietary allowance is 600 IU (15 mcg) per day, rising to 800 IU past 70 - and the Food and Nutrition Board set those numbers assuming you get essentially no sun, so they are a floor you can hit indoors in January, not a tan-dependent target. The same authority caps adults at 4,000 IU per day, which matters more than the RDA does, because vitamin D is the fat-soluble vitamin people most reliably overdose with pills.
The math and the mix are simpler than the marketing. Every mcg equals 40 IU - the two units on labels are the same molecule wearing different outfits, so a 25 mcg capsule is 1,000 IU and nothing more. Food rarely closes the gap: NHANES data show 92% of men and more than 97% of women take in less than 400 IU per day from food and beverages alone, which is why fortified milk (about 120 IU a cup) and fatty fish matter, and why the table below lists the actual leaders - cod liver oil at 1,360 IU a tablespoon sits at the top for a reason.
The winter angle is real but narrower than it feels. Sun below roughly 42 degrees elevation carries too little UVB for the skin to synthesize anything, so from November through February much of the continental US makes vitamin D the same way Alaska does: from a bottle. What sun cannot be replaced by is a window - UVB does not pass through glass, so the office-corner 'sunny desk' produces zero of it. The tables below give you the age ladder, the food ladder, and the blood-level bands, all from the NIH Office of Dietary Supplements' professional fact sheet.
How to use
- Read your row: find your age band in the RDA table, note the IU figure, and compare it to your supplement - remembering the 40-IU-per-mcg conversion so a '25 mcg' capsule reads as 1,000 IU, not some stronger mystery dose.
- Check the ceiling in the same row: infants cap at 1,000-1,500 IU (the steepest limit in the table, because breast milk plus drops plus fortified formula stack quietly), children at 2,500-3,000 IU, and everyone 9 and older at 4,000 IU per day.
- Close the gap with the food table before the pill bottle: one tablespoon of cod liver oil or a serving of salmon or UV-exposed mushrooms moves real numbers; a serum 25(OH)D test, read against the status bands, tells you whether any of it worked.
Frequently asked questions
How much vitamin D should I take per day?
By the NIH RDA: 400 IU is the adequate intake for infants under 1, 600 IU per day covers everyone from age 1 through 70, and 800 IU is the recommendation past 70 - when skin synthesis drops anyway. Pregnancy and breastfeeding do not raise the number: it stays 600 IU. The Institute of Medicine built the figure assuming minimal sun exposure, so you do not add a correction for winter or sunscreen; you treat the RDA as the total target.
What is the upper limit, and what happens if I exceed it?
The tolerable upper intake level is 1,000 IU for infants 0-6 months, 1,500 IU from 7-12 months, 2,500 IU for ages 1-3, 3,000 IU for 4-8, and 4,000 IU per day for everyone 9 and older. Chronically exceeding it raises serum 25(OH)D above 125 nmol/L, where the documented risks are hypercalcemia - nausea, vomiting, kidney stones, and in extreme cases kidney damage - which is why the 'more is better' shelf of the supplement aisle is the one to skip.
Is vitamin D3 better than D2?
For raising and holding your blood level, yes - head-to-head trials and the meta-analysis behind the NIH write-up found D3 (cholecalciferol, from animal sources or UV-treated lichen) more effective at increasing serum 25(OH)D than D2 (ergocalciferol, the plant/fungal form), and it keeps the level stable longer. Either form counts toward the RDA, but when the label gives you the choice, D3 is the one that does the job at the dose printed on it.
What should my vitamin D blood level be?
The NIH bands: below 30 nmol/L (12 ng/mL) is deficiency, associated with rickets in children and osteomalacia in adults; 30 to below 50 nmol/L is generally viewed as inadequate for bone and overall health in most people; 50 to 125 nmol/L (20 to 50 ng/mL) is generally adequate; and above 125 nmol/L is where adverse effects become a concern. Labs may print a different 'optimal' range on the report - the NIH bands are the conservative, evidence-reviewed ones.
Can I get vitamin D through a window or on a cloudy day?
Through glass, no: window glass blocks the UVB wavelengths the skin needs to make vitamin D entirely, so a sunny windowsill produces none. Cloudy days and shade cut UVB by more than half but do not zero it, and no synthesis at all happens from November through February at US latitudes above roughly 37 degrees north, because the sun never climbs high enough. That seasonal cliff - not daily weather - is the argument for knowing the food and supplement rows of this table.
Do I need a vitamin D supplement in winter?
The honest framing from the 2024 Endocrine Society guideline: routine supplementation is suggested for children 1-18, adults over 75, pregnant people, and those with prediabetes - and explicitly not recommended as routine for healthy adults 19-74, where the trials found no clear benefit. Food plus 600 IU from a standard multivitamin or vitamin D pill covers the sunless months without approaching the 4,000 IU ceiling; what you should not do is megadose, because the deficiency-to-toxicity window is measured in months of excess, not single pills.