Vitamin D is a fat-soluble vitamin, meaning that it does not dissolve in water and is absorbed best in your bloodstream when paired with high-fat foods.

For this reason, it’s recommended to take vitamin D supplements with a meal to enhance absorption.

According to one study in 17 people, taking vitamin D with the largest meal of the day increased vitamin D blood levels by about 50% after just 2–3 months (NIH).

In another study in 50 older adults, consuming vitamin D alongside a fat-heavy meal increased vitamin D blood levels by 32% after 12 hours compared to a fat-free meal (NIH).

Avocados, nuts, seeds, full-fat dairy products and eggs are nutritious sources of fat that help boost your vitamin D absorption.

Types of Vitamin D

There are two main dietary forms (NIH):
Vitamin D3 (cholecalciferol). Found in some animal foods, like fatty fish and egg yolks.
Vitamin D2 (ergocalciferol). Found in some plants, mushrooms, and yeasts.

Difference between vitamin D and D3? Of the two, D3 (cholecalciferol) seems to be almost twice as effective at increasing blood levels of vitamin D as D2 (ergocalciferol) (NIH, NIH).

In the US, current guidelines suggest that consuming 400–800 IU (10–20 mcg) of vitamin D should meet the needs of 97–98% of all healthy people (Trusted Source).

However, many experts believe the guidelines are far too low (Trusted Source).

Your vitamin D needs depend on a variety of factors. These include your age, skin color, current blood vitamin D levels, location, sun exposure and more.

To reach blood levels linked to better health outcomes, many studies have shown that you need to consume more vitamin D than the guidelines recommend (Trusted Source, Trusted Source, Trusted Source).

For instance, an analysis of five studies examined the link between vitamin D blood levels and colorectal cancer (Trusted Source).

Scientists found that people with the highest blood levels of vitamin D (over 33 ng/ml or 82.4 nmol/l) had a 50% lower risk of colorectal cancer than people with the lowest levels of vitamin D (less than 12 ng/ml or 30 nmol/l).

Research also shows that consuming 1,000 IU (25 mcg) daily would help 50% of people reach a vitamin D blood level of 33 ng/ml (82.4 nmol/l). Consuming 2,000 IU (50 mcg) daily would help nearly everyone reach a blood level of 33 ng/ml (82.4 nmol/l) (Trusted Source, Trusted Source, Trusted Source).

Deficiency: Less than 20 ng/ml (50 nmol/L)
Insufficiency: 21 – 29 ng/ml (52 – 72 nmol/L)
Sufficiency: More than 30 ng/ml (75 nmol/L)

Another analysis of seventeen studies with over 300,000 people looked at the link between vitamin D intake and heart disease. Scientists found that taking 1,000 IU (25 mcg) of vitamin D daily reduced heart disease risk by 10% (Trusted Source).

Based on current research, it seems that consuming 1,000–4,000 IU (25–100 mcg) of vitamin D daily should be ideal for most people to reach healthy vitamin D blood levels.

However, don’t consume more than 4,000 IU of vitamin D without your doctor’s permission. It exceeds the safe upper limits of intake and is not linked to more health benefits (Trusted Source).

To maintain healthy levels, only 400 to 800 IU (15 to 20 mcg) of vitamin D is required daily, but, to boost low levels, higher doses, such as 2,000 IU daily, are used and are generally safe.

Vitamin D deficiency is one of the most common nutrient deficiencies.

Some people are at a greater risk than others. In the United States, 41.6% of the total population is deficient, although minorities fare worse — 82.1% and 69.2% of blacks and Hispanics are deficient, respectively (Trusted Source).

Additionally, older adults are at a much greater risk of being deficient (Trusted Source).

Those who have certain diseases are also very likely to be deficient. One study showed that 96% of people who had experienced heart attacks were low in vitamin D (Trusted Source).

Overall, vitamin D deficiency is a silent epidemic. The symptoms are usually subtle and may take years or decades to surface.

The most well-known symptom of vitamin D deficiency is rickets, a bone disease common in children in developing countries.

Rickets has been mostly eliminated from Western countries because of the fortification of some foods with vitamin D (Trusted Source).

Deficiency is also linked to osteoporosis, reduced mineral density, and increased risk of falls and fractures in older adults.

What’s more, studies indicate that people with low vitamin D levels have a much greater risk of heart disease, diabetes (types 1 and 2), cancer, dementia, and autoimmune diseases like multiple sclerosis (Trusted Source).

Finally, vitamin D deficiency is linked to a reduced life expectancy (Trusted Source, Trusted Source, Trusted Source).

Taking vitamin D3 and K2 together actually promotes new bone growth. In 2019, researchers observed that vitamin D3 and K2 worked in tandem to form new osteoblasts, the cells that secrete osteocalcin, which is a biomarker for new bone growth.

Eggs (44 IU per egg), along with fortified foods including milk and some cereals are excellent sources. 

The best form of vitamin D to take is D3. It’s the form that is most closely related to the same vitamin the human body creates. And with natural sources being quite limited, it’s often best to take vitamin D3 supplements.

Here is the vitamin D3 content of a few of the best food sources (NIH):