What is vitamin D good for?

What is vitamin D good for? This vital vitamin is important for the development of bones and your immune system

Two people taking vitamin D supplements
(Image credit: Getty Images)

What is vitamin D good for and do you really need it? Well, during the darkest months of the year, you may wonder if you’re getting enough vitamin D, which your body produces naturally when exposed to sunlight.

If you're considering taking the best vitamin D supplements or other vitamins to help you feel your best, but when it comes to vitamin D, it can be confusing to know where to start getting the right dose. 

The National Institutes of Health state that vitamin D has several essential functions. Together with calcium, vitamin D helps protect you from developing osteoporosis. Your immune system also needs vitamin D to fight invading bacteria and viruses.

Your body makes vitamin D when your bare skin is exposed to the sun, and most people get at least some vitamin D this way. However, clouds and smog reduce the amount of vitamin D your skin makes because you’re not exposed to as much sunlight.

So, If you’re not getting enough vitamin D from natural sources, you may need to take a supplement or consider one of the best SAD lamps which mimic natural sunlight.

Where do you get vitamin D?

Woman bathing in sunlight

(Image credit: Getty Images)

Vitamin D is a fat-soluble vitamin naturally present in a few foods, added to other foods and beverages, and is available as a dietary supplement. It is also produced when sunlight's ultraviolet (UV) rays strike the skin and trigger vitamin D synthesis.

During the spring and summer months, with longer sunlight hours, most people should be able to make all the vitamin D they need from sunlight. However, during the winter months, the lack of sunlight and wearing clothes that cover the skin from direct UV rays may mean that you don’t make enough vitamin D. 

Very few foods naturally contain vitamin D. Thankfully, there are foods available that are fortified with vitamin D. Be sure to check the label of the food and beverages you consume for the amount of vitamin D. As per the National Institutes of Health Office of Dietary Supplements:

  • Almost all U.S. milk supply is fortified with about 3 mcg (120 IU) of vitamin D per cup. In addition, many plant-based alternatives such as soy milk, almond milk, and oat milk are similarly fortified.
  • Vitamin D is added to many breakfast cereals and some orange juice brands, yogurt, margarine, and other food products.
  • Fatty fish (like trout, salmon, tuna, and mackerel) and fish liver oils are among the best natural sources of vitamin D.
  • Beef liver, egg yolks, and cheese have small amounts of vitamin D.
  • Mushrooms provide a little vitamin D. Some mushrooms have been exposed to ultraviolet light to increase their vitamin D content.

What are the benefits of vitamin D?

Scientists are studying how vitamin D affects health. So far, research has shown that vitamin D plays a role in the following conditions:

Bone health

Long-term shortages of vitamin D and calcium cause your bones to become fragile and break more easily (a condition called osteoporosis). Getting recommended amounts of vitamin D and calcium from foods (and supplements) will help maintain healthy bones and prevent osteoporosis.

Multiple Sclerosis (MS)

In 2015, scientists demonstrated a clear link between low vitamin D and MS. In addition, they found that people who naturally had lower vitamin D levels (because of genetic factors) were more likely to develop MS. However, it’s worth noting that researchers are still unsure of what causes the link between vitamin D and MS, and more research is needed in this area. 

Heart disease

Low vitamin D levels have been linked to an increased risk of heart diseases such as hypertension, heart failure, and stroke. But it’s unclear whether vitamin D deficiency contributes to heart disease or is a marker of poor health in chronic disease. Some studies show that vitamin D supplements might help reduce blood cholesterol levels and high blood pressure—two of the main risk factors for heart disease. However, other studies show no benefits.


Vitamin D is needed for your brain to function properly. Some studies have found links between low blood levels of vitamin D and an increased risk of depression. A systemic review of 7,534 people found that those encountering negative emotions who received vitamin D supplements noticed an improvement in symptoms. Vitamin D supplementation may help people with depression who have a vitamin D deficiency. Another study identified low vitamin D levels as a risk factor for more severe fibromyalgia symptoms, anxiety, and depression.

How much vitamin D do you need?

In healthy people, the amount of vitamin D needed per day varies by age. The information below is from the Institute of Medicine, now the Health and Medicine Division of the National Academies of Sciences, Engineering, and Medicine. If your doctor checks your blood levels, they might recommend higher doses based on individual needs. 

The Recommended Dietary Allowances for vitamin D are as follows:

  • infants (0–12 months): 10 mcg (400 IU)
  • children and teens: 15 mcg (600 IU)
  • adults ages 18–70: 15 mcg (600 IU)
  • adults over age 70: 20 mcg (800 IU)
  • pregnant or breastfeeding women: 15 mcg (600 IU)

Sometimes, you can get too much of a good thing with vitamin D. Very high levels of vitamin D in your blood (greater than 375 nmol/L or 150 ng/mL) can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones.

High vitamin D levels are almost always caused by consuming excessive vitamin D from dietary supplements. You cannot get too much vitamin D from sunshine because your skin limits the amount of vitamin D it makes, however, it’s always best to protect your skin from damage by wearing sunscreen.

If you do need to top up your levels, you don't have to take supplements. But before you start looking at alternatives, it's worth finding out do vitamin patches work?

Catherine Renton

Catherine is a freelance journalist writing across titles such as Verywell Health, Healthline, The Daily Telegraph, Refinery29, Elle, and Vogue. She specializes in content covering health, fitness, wellness, and culture. A once reluctant runner, Catherine has competed in 30 running events in the past five years and looks forward to one day running the London Marathon.