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- Vitamin D3, a form of vitamin D, promotes strong bones, good immune health, and mental well-being.
- You can get vitamin D3 from fortified foods, eggs, and fatty fish — or by spending time in the sun.
- Supplements can help you meet your daily needs, but stick to the RDA to avoid serious side effects.
Vitamin D3 plays an important role in the strength of your bones. It also bolsters your immune system and supports mental well-being.
You get this essential vitamin from:
- Oysters
- Fatty fish like salmon and tuna
- Pork
- Egg yolks
- Fortified plant milk and dairy products, like milk, yogurt, and some cheeses
- Fortified orange juice and breakfast cereals
You can also get plenty of vitamin D3 simply by stepping outside — your body synthesizes this vitamin when your skin is exposed to sunlight.
Here are some benefits of vitamin D, along with how much you need and when to supplement.
Is vitamin D the same as D3?
Vitamin D3 and its counterpart, D2, are both forms of vitamin D.
- Vitamin D2: Found in plant sources, mushrooms and yeast, and supplements
- Vitamin D3: Found in animal products and produced by your body from sunlight
Both types of vitamin D provide the same benefits and contribute to your overall vitamin D level.
That said, when it comes to selecting a supplement, you’ll always want to choose D3 over D2.
Vitamin D3 is easier for the body to absorb, so it raises your vitamin D levels more effectively, says Taylor Moree, a registered dietician at The Nutrition Clinic for Digestive Health.
What is vitamin D3 good for?
Vitamin D has multiple positive effects on your physical and mental health, including:
Supporting healthy bones
Vitamin D helps your body absorb calcium and phosphorus — both of which promote bone health. Vitamin D also regulates and stimulates osteoblasts, the cells responsible for bone formation.
Without adequate vitamin D, you wouldn’t be able to absorb enough calcium to maintain your bone density, and calcium deficiency may raise your risk of osteopenia and osteoporosis.
A lack of vitamin D can also lead to rickets, a condition that causes weakening and softening bones in children.
Reducing depression
Studies have linked low levels of vitamin D to depression, though the exact link between vitamin D and depression remains unclear.
Simply put, experts don’t know whether low levels of vitamin D directly contribute to depression — or if certain factors, like a lack of sunlight or a diet that lacks key nutrients, independently contribute to both depression and vitamin D deficiency.
That said, some research does suggest vitamin D supplements may help ease depression. A 2019 review analyzed 4 studies with a total of 948 participants who had depression and concluded that vitamin D supplements had a moderate effect on reducing depression symptoms.
However, results from other studies on vitamin D and depression are mixed, with some research suggesting vitamin D supplements do little to improve depression symptoms.
Future research may help shed more light on the connection between vitamin D and depression and the potential benefits of supplements.
Regulating the immune system
Vitamin D supports your immune system by regulating B and T cell production — the cells that eliminate pathogens — and by supporting cells that fight off bacteria and fungi.
More research is needed, but taking a vitamin D supplement could offer some protection during flu season by lowering your risk of upper respiratory infections.
Vitamin D may also play a part in autoimmune disease, conditions where your immune system becomes overactive and attacks your body.
Experts have linked low levels of vitamin D to both onset and progression of:
On the flip side, vitamin D supplements may help lower your risk of these conditions.
A large study from 2019 monitored 25,871 people over the course of five years. In that time, some took vitamin D supplements with or without fish oil, some took fish oil only, and some took a placebo. The participants who took vitamin D had a 22% reduced rate of autoimmune disease after five years, compared to the placebo group.
It may lower your risk of cancer
Some research suggests low levels of vitamin D may increase your risk of cancer. Other research suggests you’re less likely to die from cancer if you have high vitamin D levels.
The role of vitamin D and cancer has been studied most often in colorectal, breast, prostate, and pancreatic cancer. Research suggests vitamin D may offer some protective benefits for each of these types of cancer, with colorectal cancer having the strongest evidence base.
However, not all studies agree. Experts have found conflicting evidence for how much vitamin D might influence cancer, so further research may yield more insight.
How much vitamin D3 do you need daily?
An estimated 40% of adults in the US and about 15% of children have a vitamin D deficiency.
The recommended dietary allowance (RDA) of vitamin D is:
- For infants 0-12 months: 10 micrograms (mcg), or 400 international units (IU)
- For people ages 1-70: 15 mcg (600 IU) per day
- For people over age 70: 20 mcg (800 IU)
It can be difficult to get enough vitamin D from food, especially if you:
- eat a vegan diet
- Have allergies to foods that contain high amounts of vitamin D
- Have a health condition that affects your body’s ability to absorb vitamin D
But spending time in bright sunlight three days a week, with your arms and legs exposed, is typically enough to help you avoid vitamin D deficiency. You’ll need to spend about 15 minutes in the sun at a time if you have light skin and about 25 minutes if you have darker skin.
Important: Sunscreen, higher latitudes, and aging all decrease your absorption of vitamin D from the sun. If spending time in the sunlight doesn’t seem to help raise your vitamin D levels, you may want to focus on dietary or supplemental sources of vitamin D instead.
When you might need to supplement
People most likely to have a vitamin D deficiency include:
- Breastfed infants: Human milk alone may not meet infants’ vitamin D needs — the American Academy of Pediatrics recommends breastfed or partially breastfed infants be given 400 IU per day of vitamin D supplements, in liquid form, starting in the first few days of life.
- Older adults: Your body’s ability to make vitamin D from sunlight decreases with age. Plus, older adults who spend more time indoors also have an increased risk of vitamin D deficiency.
- People with darker skin: Higher amounts of melanin — the pigment that gives your skin its color — reduce the amount of vitamin D your body can produce from sunlight. Thus, people with darker skin often have lower vitamin D levels. In fact, Black Americans have 15 to 20 times the rate of vitamin D deficiency than white Americans.
- People with certain digestive conditions: If you have a health condition that affects your ability to digest fat, such as Crohn’s disease, ulcerative colitis, or celiac disease, you may not be able to absorb enough vitamin D to meet the RDA.
Supplementing with 1000 to 2000 IU per day is generally safe for adults and can help raise vitamin D to recommended levels.
Quick tip: Always combine vitamin D supplements with a dietary fat because fat increases vitamin D absorption, says Moree. For instance, you might take your supplement with a meal that includes oil, nuts, avocado, or fatty fish.
Just make sure to talk to a healthcare professional before you try vitamin D or D3 supplements — they’ll want to check your levels beforehand, says Jen Hernandez, a registered dietician and founder of Plant-Powered Kidneys.
Your doctor can offer more guidance about increasing your vitamin D3 intake via dietary sources or supplements.
Note: Vitamin D3 typically isn’t HSA or FSA-eligible, though it may qualify if your doctor provides a letter of medical necessity.
Can you get too much vitamin D3?
Vitamin D is a fat-soluble vitamin — these types of vitamins remain in your body, in fatty tissue and in your liver.
Because your body stores vitamin D, you can consume too much of it. Daily doses that exceed 50,000 IU — more than 80 times the RDA — may cause hypercalcemia, a buildup of calcium in the body.
Hypercalcemia can cause:
- Nausea and vomiting
- Loss of appetite
- Excessive thirst
- Muscle weakness
- Pain
- Dehydration
- Kidney stones
Very high levels of vitamin D can cause more severe side effects like kidney failure, irregular heartbeat, and even death.
If you suspect you may have consumed too much vitamin D, check in with your doctor — they can order a blood test to check your vitamin D levels.
Important: Make sure to talk with your provider before taking vitamin D if you take statin medications or thiazide diuretics. Vitamin D can reduce statin’s effectiveness, and it may cause hypercalcemia when taken with thiazide diuretics.
Insider’s takeaway
Vitamin D3, one form of vitamin D, is important for your bones, immune system, and mental health — it may even play a role in preventing cancer.
Plenty of people don’t get enough vitamin D on a regular basis, but you can easily take steps to boost your intake by catching some sunshine.
If you think you may not get enough vitamin D from either your diet or the sun, you can also ask your doctor if a vitamin D supplement could have benefits.
