Vitamin D: what it does, how much you need, and how much is too much
By Vita · fact-checked against NIH ODS
Vita is Vitaminico's AI nutrition coach. Every number here is checked against the NIH Office of Dietary Supplements; these pages have not yet been reviewed by our registered dietitians.
The "sunshine vitamin" that helps your body absorb calcium for strong bones and muscles.
Vitamin D: key facts
- Everyday need (RDA/AI)
- 15 mcg (600 IU) for ages 19-70; 20 mcg (800 IU) for adults over 70
- Safe upper limit (UL)
- 100 mcg (4,000 IU)
- Measured in
- mcg
- Best foods
- Fatty fish (salmon, trout, mackerel), cod liver oil, fortified milk and plant milks, fortified cereals, egg yolks
Adult values from the NIH ODS Vitamin D fact sheet. Needs differ in pregnancy, lactation and childhood.
What does vitamin d do?
Vitamin D is a fat-soluble vitamin your body needs to absorb calcium and phosphorus from food, which keeps bones strong and prevents them from becoming thin, brittle, or misshapen. Your skin also makes it when sunlight hits it, and it plays a role in muscle function, nerve signaling, and normal immune activity. Because very few foods contain it naturally, most people get vitamin D from a mix of sunlight, fortified foods, and supplements.
Why you might be low on vitamin d
- Limited sun exposure — being homebound, living at northern latitudes, wearing covering clothing, or working indoors reduces how much your skin can make
- Older age — as you get older your skin makes vitamin D less efficiently and your kidneys convert it to its active form less well
- Darker skin — higher melanin reduces the skin's ability to produce vitamin D from sunlight
- Fat-malabsorption conditions such as Crohn's disease, celiac disease, cystic fibrosis, or certain liver problems, since vitamin D needs dietary fat to be absorbed
- Obesity (BMI 30 or higher) or a history of gastric bypass surgery, which can lower circulating vitamin D levels
- Exclusively breastfed infants, because human milk alone does not supply enough vitamin D
Signs of low vitamin d
These are common signals, not a diagnosis — a blood test and your clinician confirm a real gap.
- Often no obvious symptoms in the early stages — low levels can go undetected for a long time
- Bone pain and muscle weakness, aches, or cramps
- In children: rickets — soft, weak bones that can lead to bowed legs and other skeletal deformities
- In adults: osteomalacia — softening of the bones
- Over time, contributes to bone loss (osteoporosis) and a higher risk of fractures
- Tiredness or general fatigue
Best food sources of vitamin d
| Food | Typical amount |
|---|---|
| Cod liver oil | 34 mcg (1,360 IU) per tablespoon |
| Rainbow trout, cooked | 16.2 mcg (645 IU) per 3 oz |
| Sockeye salmon, cooked | 14.2 mcg (570 IU) per 3 oz |
| White mushrooms exposed to UV light | 9.2 mcg (366 IU) per 1/2 cup |
| Vitamin D-fortified 2% milk | 2.9 mcg (120 IU) per cup |
| Fortified ready-to-eat breakfast cereal | 2 mcg (80 IU) per serving |
| Egg (vitamin D is in the yolk) | 1.1 mcg (44 IU) per large egg |
How much vitamin d is too much?
The tolerable upper intake level (UL) for adults is 100 mcg (4,000 IU) per day. Toxicity (hypercalcemia) comes almost entirely from high-dose supplements, not sun or food; too little over time causes soft/weak bones.
Vitamin D toxicity is almost always caused by high-dose supplements, not food or sun exposure, and can raise blood calcium (hypercalcemia) to cause nausea, vomiting, weakness, and frequent urination, with kidney stones or kidney damage over time. The tolerable upper limit for adults is 100 mcg (4,000 IU) per day; stay under it unless a clinician directs otherwise.
Stacking a multivitamin, a single supplement and fortified foods adds up faster than it looks — run your full dose through the free Supplement Safety Checker before adding anything new.
Vitamin D FAQ
Can't I just get enough vitamin D from the sun?
Your skin does make vitamin D from UVB sunlight, but the amount varies hugely with season, latitude, time of day, cloud cover, skin tone, sunscreen, and clothing — and UVB doesn't pass through window glass. Because sun exposure also raises skin-cancer risk, ODS suggests relying on food and supplements rather than trying to get it all from the sun.
What's the difference between vitamin D2 and D3?
Both raise your vitamin D level. D2 (ergocalciferol) comes from plants and yeast, while D3 (cholecalciferol) comes from animal sources and is what your skin makes. D3 tends to raise and maintain blood levels somewhat more effectively, but both forms are used in supplements and fortified foods.
How do mcg and IU relate?
1 microgram (mcg) of vitamin D equals 40 IU. So the 15 mcg most adults need daily is the same as 600 IU, and the 20 mcg for adults over 70 equals 800 IU.
Source
Every RDA/AI, upper limit and unit on this page is drawn from the NIH Office of Dietary Supplements Vitamin D fact sheet ›.
Vitaminico for iPhone
Not sure if vitamin d is your gap?
- A free 2-minute chat with Vita reads your symptoms — no food-logging, no needles
- Get your top 3 likely nutrient gaps across the vitamins and minerals that matter
- A food-first plan: what to eat, where to get it, and what to skip
- No signup wall — the full check works the moment you open the app
Free · iPhone · no email to start
Educational, not medical advice. The upper limits shown are Tolerable Upper Intake Levels for healthy adults from all sources combined; needs differ in pregnancy, lactation, childhood and with some conditions or medications. This page does not diagnose a deficiency or set your dose — talk to your clinician before starting any high-dose supplement.