Medically Reviewed

How Long Does It Take for Vitamin D to Work? What to Expect

Vitamin D deficiency is quite common. More time in the sun can help increase levels, but how long will it take to get your vitamin D up to a healthy level?

Vitamin D is often called the “sunshine vitamin” because the body needs UV radiation from the sun’s rays to produce it. If you’ve made lifestyle changes in order to help improve your levels of the vitamin, you might be wondering how long it will take to see results. You might also ask: “How long should I take a vitamin D supplement?” We’re investigating those questions to find out more about this commonly deficient vitamin.

Symptoms of low vitamin D

Vitamin D is a fat-soluble vitamin that supports bone health, immune function, and countless other systems of the body. Vitamin D deficiency had been a serious issue prior to the mass fortification of foods like milk and other dairy products. It still is common throughout the world. While rare, severe vitamin D deficiency can result in rickets. Vitamin D was traditionally used years ago to treat rickets. Because vitamin D plays an important role in helping our bodies absorb calcium, bone weakening is a major concern for people with low levels. Other symptoms of low levels of vitamin D may include:

  • Fatigue
  • Trouble sleeping
  • Hair loss
  • Muscle weakness
  • Weakened immune system

You can have your blood levels checked if you believe your amounts of vitamin D may be low. It’s important to note, however, that because vitamin D supplementation doesn’t carry risks and is often recommended, this may be an easier solution. One study noted a strain placed on health care resources as more patients exponentially seek vitamin D blood tests.

Who is at risk for a vitamin D deficiency?

Since sunlight is an excellent source of vitamin D, people who do not get enough sun exposure may be at risk for low vitamin D levels. This includes people who use sunblock regularly, as sunscreens are formulated to block UVB radiation, which is what the body needs to synthesize vitamin D. Also, people who have darker skin may have more of a challenge absorbing UVB rays because of the higher levels of melanin in their skin, which can act as a natural sunblock allowing for less absorption of UV radiation.

Other people who may be at risk for a vitamin D deficiency include people who typically cover their body in clothing and people who do not go outside often, since UVB radiation cannot penetrate through windows in offices, homes, or cars. Living in an area with high pollution or a geographic location with a high latitude, where the sun’s rays are the weakest, may also be at risk for low levels of vitamin D. Finally, people who are lactose intolerant or have digestive issues with processing fats may have vitamin D deficiency since absorption of fat-soluble vitamin D may be more difficult.

Best ways increase your levels of vitamin D

There are many options to increase your vitamin D levels. Here we’ll explore the three most common and effective ways of adding a larger dose of vitamin D to your life.


Sunlight is one of the most accessible sources of vitamin D. It’s free and can typically be accessed every day. Exposing at least 40% of skin, not covered by clothing or sunblock, to about 15 to 30 minutes of sunlight every other day is a good way to get the UVB radiation necessary for vitamin D synthesis in the body.

Yes, UVB radiation is in the same type of sunlight we’ve been warned about for the damage it can do to our skin. Since sun exposure can cause premature aging as well as other health risks, it’s essential to moderate our exposure. Don’t remain in the sun for too long. If your skin is red or sunburnt after your sunlight session, you may be staying in the sun for too long.


Only a small variety of foods naturally contain vitamin D and the amounts are generally small. Diet should be looked at as a supportive way to add vitamin D to your body, but not as the primary method. Foods like the below list contain both vitamin D2 and vitamin D3, which are similarly absorbed and processed by the body.

Fortified foods, like whole milk with vitamin D added, can provide a useful source. Remember, since vitamin D is fat-soluble, it requires fat to be absorbed, which is why it is often added to dairy products.

Foods that contain vitamin D:

  • Cod liver oil
  • Rainbow Trout
  • Sockeye Salmon
  • White Mushrooms, exposed to UV light
  • Plant-based milks fortified with vitamin D
  • Cereals fortified with vitamin D
  • Sardines
  • Eggs

Vitamin D supplements

Vitamin D in the form of dietary supplements is recommended as a way to ensure your body gets adequate levels of vitamin D. These supplements are best taken with food, particularly foods which contain fat. This is often why you’ll see vitamin D supplements paired with the largest meal of the day to aid in absorption. This has been shown to actually increase levels by as much as 50%.

Between 25-50mcg (1,000-2,000 IU) is a good range of vitamin D to take on a daily basis for supportive maintenance. It’s a good idea to consult your healthcare provider before beginning any supplementation or considering larger doses. Your healthcare provider can help you to determine which dosage is appropriate for your body’s specific needs. Care/of offers two vitamin D supplements, the Sunny D3 option is vegetarian and non-GMO and the vegan formulation is made from sustainable algae. Both provide 25mcg (1000 IU) of Vitamin D3.

How long does it take for vitamin D to work?

Vitamin D doesn’t offer an overnight change. In fact, the one study showed that the largest increase in vitamin D levels came between three to nine months after beginning supplementation. research showed that adding vitamin D supplements can be expected to raise the vitamin D level, measured as serum 25(OH)D, by about 1 ng/mL for every 2.5mcg (100 IU) of additional vitamin D each day.

Since everyone’s body is different, there’s no strict guideline on when you will notice results from vitamin D supplements. How long it takes to see results is largely dependent on where your vitamin D levels were prior to supplementing and how well your body absorbs the nutrient. If you have a clinical deficiency, you may notice positive effects shortly after beginning a vitamin D supplement. Consistency is key to seeing positive results and supplements should be taken daily for noticeable change.

How long should you continue taking a vitamin D supplement?

Supplementing with vitamin D can have beneficial effects when done consistently each day. Since the main source of vitamin D is the sun’s rays, it’s especially important to supplement during times of less sunlight. This could mean supplementing with vitamin D during the fall and winter months and taking a break during the summer, particularly if you spend significant time outdoors and in the sun. It’s best to talk to your doctor to develop a vitamin D supplement plan that’s right for you. Since there are very few side effects or reasons not to take vitamin D, it’s an easy choice to make it a part of your wellness routine.

Key takeaways

The sun’s UVB radiation helps our bodies to produce vitamin D.

There are many factors that can make UVB absorption difficult. These include artificial barriers to UVB absorption, like sunblock and clothing, or naturally-occuring reasons, like high skin melanin levels and living in a geographic location where the sun is less intense.

It’s common to have low levels of vitamin D, which can cause fatigue and mood changes, as well as issues with bones, muscles, and the immune system.

Supplementing with a vitamin D supplement can help ensure you get enough of the nutrient, since vitamin D does not naturally occur in many foods.

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