How can I raise my vitamin D levels quickly?

You can raise your vitamin D levels quickly in three main ways, but it can take up to a week for increased vitamin D intake or exposure to be reflected in a vitamin D blood test:

• Increasing your intake of foods that are naturally rich in vitamin D or fortified with vitamin D
• Taking a vitamin D supplement
• Getting outside and exposing your skin to sunlight (although experts do not recommend this without sun protection).

Eat foods rich in vitamin D or fortified with vitamin D

Increasing your intake of foods and beverages that contain vitamin D is an option if you're looking to boost your vitamin D levels. Foods that may help boost your vitamin D levels are:

• Cod liver oil*
• Trout*
• Salmon*
• Mushrooms*
• Fortified dairy and non-dairy milks
• Fortified cereals
• Sardines
• Eggs
• Liver
• Cheese.

*These foods provide 20% or more of your daily value of vitamin D per serving, and are considered high sources of vitamin D.

Foods such as cow's milk, soy milk, orange juice, cereals, and oatmeal are sometimes fortified with vitamin D; look on the label to be sure.

Try supplements, with your doctor’s supervision

The easiest and most efficient way to increase vitamin D levels may be to take supplements. Considering the skin cancer risks of using sunlight to boost vitamin D and the difficulty of getting enough vitamin D in your diet, supplements are often the primary recommendation for people who are deficient in vitamin D.

Vitamin D can be found in many multivitamin supplements, but it can also be taken on its own. There are two types of vitamin D: D2 and D3. Both types are available in supplement form, and their effect on overall vitamin D levels is roughly equivalent. However, some research has indicated that D3 may lead to a greater and more sustained elevation of vitamin D in the blood than D2.

Various studies have estimated that it takes up to 24 hours for vitamin D3 supplements to raise vitamin D levels in the bloodstream. However, vitamin D then needs to be converted to its active form (calcitriol, also called 1,25-dihydroxycholecalciferol or 25(OH)D). After taking a high dose of vitamin D3, a study showed it can take approximately seven days for it to convert and cause a peak in 25(OH)D levels, the form tested by your doctor.

Since vitamin D is fat-soluble, the process of absorbing and converting vitamin D is aided by fat. It is helpful to take vitamin D alongside a meal that contains fat. People with health conditions like Crohn's disease, celiac disease or ulcerative colitis may have difficulty absorbing vitamin D because their condition affects the ability to absorb fat. These groups are among those who are more at risk of developing vitamin D deficiency, along with breastfed babies and people who are older, avoid the sun, have dark skin, are obese or have had gastric bypass surgery.

The critical takeaway is that vitamin D levels increase gradually. If a test reveals that your vitamin D levels are low, you'll need to consult with a doctor to determine how much vitamin D you need to take to raise your levels and keep them up.

There are mixed views on what counts as a healthy, normal or inadequate amount of vitamin D. To test vitamin D, the concentration of hydroxyvitamin D in blood serum is measured. According to the National Institutes of Health Office of Dietary Supplements:

• A serum concentration of 50 nanomoles per liter (nmol/L) or more is generally considered normal and healthy
• A serum concentration between 30 and 50 nmol/L potentially indicates inadequate vitamin D
• A serum concentration under 30 nmol/L means vitamin D deficiency
• Measurements over 125 nmol/L may be too high and are associated with health risks.

While there is much debate about how much vitamin D people need, the Office of Dietary Supplements says:

• The recommended daily intake for adults is 600 IU (15 mcg).
• Older adults over the age of 70 should aim for 800 IU (20 mcg) daily.
• People deficient in vitamin D may need to take higher doses, but these decisions should be made with your doctor.
• Taking vitamin D supplements containing over 4,000 IU is not advisable without medical supervision.

Sunlight can boost vitamin D but you need to be careful

Vitamin D3 from the sun’s rays has been shown to last longer in your body than the vitamin D3 from food or supplements. But because sun exposure is associated with skin cancer, the American Academy of Dermatology (AAD) does not recommend getting vitamin D from sun exposure or sunbeds.

The AAD recommends getting vitamin D from foods naturally rich in vitamin D, foods and beverages fortified with vitamin D, and/or vitamin D supplements.

How does your skin make vitamin D?

When the UVB rays in sunlight hit your skin, a chemical process is triggered that ultimately results in the production of vitamin D from a precursor form of vitamin D. It takes an estimated 8 hours for this precursor to be converted into vitamin D3, which then binds to a protein that brings it to your liver. Then, there are a few other steps before this vitamin D can be turned into the vitamin's active form in your blood, called hydroxyvitamin D. When you get your vitamin D levels tested, it is hydroxyvitamin D that is measured.

People with darker skin tones do not tend to make as much vitamin D with the same amount of sun exposure as people with lighter skin tones.