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What holds a lot of vitamin D?

Vitamin D is an essential nutrient that plays many important roles in the body. Getting enough vitamin D promotes strong bones and teeth, regulates calcium absorption, supports immune function, and protects against certain diseases like osteoporosis and some cancers. While vitamin D is found naturally in some foods, one of the best ways to get enough of this nutrient is through sun exposure. However, dietary sources are still important for those who have limited sun exposure or cannot make enough vitamin D from the sun.

What is vitamin D and why is it important?

Vitamin D is a fat-soluble vitamin that functions as a hormone in the body. There are two main forms of vitamin D: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D3 is the form made in human skin when exposed to sunlight and is also found in animal sources. Vitamin D2 occurs naturally in some plants and fungi and can also be taken as a supplement.

No matter the form, vitamin D plays several critical roles in overall health:

  • Promotes calcium absorption and bone growth – Vitamin D works with calcium and phosphorus to support bone mineralization and prevent conditions like rickets (soft, weak bones in children) and osteomalacia (soft, weak bones in adults). It helps maintain bone strength and may reduce risk of fractures.
  • Supports immune function – Vitamin D receptors are present on a number of immune cells. Getting enough vitamin D may help regulate immunity and reduce risk of illness.
  • Protects against cancer – Vitamin D may play a role in controlling cell growth and division. Adequate levels are linked to lower risk of several cancers like colorectal, breast, and prostate cancer.
  • Reduces inflammation – Vitamin D helps regulate inflammatory pathways that are implicated in conditions like inflammatory bowel disease (IBD), multiple sclerosis (MS), rheumatoid arthritis (RA), and diabetes.

Due to its far-reaching effects on health, vitamin D deficiency is associated with increased risk of bone disorders, autoimmune disease, cardiovascular disease, impaired cognition, and some cancers. Most health organizations recommend a minimum blood level of 20 ng/mL (50 nmol/L) vitamin D.

Signs and symptoms of vitamin D deficiency

The most common consequence of vitamin D deficiency is impaired bone mineralization, resulting in soft, pliable bones. In children, this can cause rickets while in adults osteomalacia occurs. Symptoms may include:

  • Bone pain
  • Muscle weakness
  • Difficulty walking
  • Bone fractures

Other signs of vitamin D deficiency include:

  • Fatigue and mood changes
  • Hair loss
  • Impaired wound healing
  • Increased infections
  • Dental problems like tooth decay

However, vitamin D deficiency often has no obvious symptoms in the early stages, which is why routine screening of blood levels is important.

How much vitamin D do you need?

The recommended dietary allowance (RDA) for vitamin D is as follows:

Age Group RDA
0-12 months 400 IU (10 mcg)
1-13 years 600 IU (15 mcg)
14-18 years 600 IU (15 mcg)
19-70 years 600 IU (15 mcg)
>70 years 800 IU (20 mcg)

Pregnant and breastfeeding women need higher amounts – at least 600 IU per day. Obese individuals may also need 2-3 times more vitamin D to meet their needs.

Many experts recommend a minimum blood level of 30-40 ng/mL (75-100 nmol/L) for optimal health. This often requires at least 1000-4000 IU per day, especially for those with limited sun exposure.

Toxicity and tolerable upper limit

Vitamin D toxicity is very rare but can occur if excessive doses over 50,000 IU per day are taken over an extended time. Symptoms may include:

  • Nausea, vomiting, poor appetite
  • Increased urination and thirst
  • High blood calcium (hypercalcemia)
  • Bone pain
  • Kidney stones

To prevent adverse effects, the tolerable upper limit for vitamin D is:

  • 0-6 months: 1,000 IU (25 mcg)
  • 6-12 months: 1,500 IU (38 mcg)
  • 1-3 years: 2,500 IU (63 mcg)
  • 4-8 years: 3,000 IU (75 mcg)
  • >8 years: 4,000 IU (100 mcg)

Food sources of vitamin D

Very few foods contain high amounts of vitamin D naturally. The top dietary sources include:

Fatty fish

Fatty fish like salmon, mackerel, sardines, and tuna are among the best natural sources. A 3.5-ounce (100-gram) serving of cooked salmon contains around 570 IU vitamin D, while canned salmon provides around 365 IU.

Fish liver oils

Fish liver oils like cod liver oil are exceptionally high in vitamin D. Just 1 tablespoon (15mL) provides over 1,300 IU.

Egg yolks

Whole eggs are a convenient source of vitamin D. Almost all the vitamin D in eggs is found in the yolk. One large egg yolk contains about 40 IU.

Mushrooms

Exposing mushrooms to UV light significantly boosts their vitamin D content. Just 3.5 ounces (100 grams) of UV-treated mushrooms can provide over 300 IU.

Fortified foods

Many common foods like cereal, yogurt, orange juice, milk, and soy milk are fortified with vitamin D. Check the label and opt for vitamin D-fortified options when possible.

Beef liver

Beef liver is one of the best sources of vitamin D from the meat aisle. A 3.5-ounce (100-gram) serving supplies around 50 IU.

Cheese

Most cheeses contain at least small amounts of vitamin D, especially hard cheeses like cheddar. One ounce (28 grams) of cheddar cheese provides around 6 IU.

Other food sources

Other foods that provide small amounts of vitamin D include egg whites, oysters, and vitamin D-fortified products like breakfast cereals, bread, orange juice, soy milk, yogurt, and margarine.

Sun exposure and vitamin D

Sunlight is a major source of vitamin D for most people. When your skin is exposed to the sun’s UVB rays, it synthesizes vitamin D.

Just 15–30 minutes per day with arms and legs uncovered can satisfy vitamin D needs for lighter-skinned people during the warmer months. Those with darker skin may need longer exposure to generate adequate vitamin D.

However, many factors affect how much vitamin D your skin makes, including:

  • Skin tone – Pale skin produces vitamin D far faster than darker skin.
  • Sunscreen – SPF 8 or more blocks over 90% of vitamin D production.
  • Latitude and season – People living farthest from the equator during the winter months produce little to no vitamin D from the sun.
  • Age – Older adults generate less efficient vitamin D production in skin.
  • Body fat – Vitamin D gets deposited into body fat stores, making it harder to maintain optimal blood levels in obesity.

Due to these factors, sunlight exposure is often insufficient to meet needs, especially during winter at latitudes above 37° north or below 37° south of the equator.

Safe sun exposure

While sunlight is the ideal way to get your daily dose of vitamin D, it’s important to avoid sunburn, which can raise skin cancer risk.

Follow these tips for safe sun exposure:

  • Limit midday sun when UV rays are strongest.
  • Wear sunscreen on your face and sensitive areas.
  • Gradually increase exposure starting in early spring.
  • Apply sunscreen 30 minutes before going outside.
  • Wear light clothing that covers skin if burning easily.
  • Stay in shade during peak hours when possible.

Should you take a vitamin D supplement?

Given the limited food sources and factors limiting vitamin D production in skin, supplements are often necessary to meet needs, especially in winter or for those with inadequate sun exposure.

Vitamin D is fat soluble, so it’s best absorbed when taken with a meal containing fat or oils. Options include vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), with research showing D3 is more potent and efficient.

Multivitamins typically provide 400–1,000 IU vitamin D, but many stand-alone supplements contain 2,000–5,000 IU per dosage.

The tolerable upper limit is 4,000 IU per day for adults, so do not exceed this dosage without medical supervision.

Those with fat malabsorption, liver disease, kidney disorders, or other conditions may require higher doses to reach optimal blood levels.

Who may need extra vitamin D?

The following groups have an increased risk of vitamin D deficiency and may need supplementation:

  • Breastfed infants
  • Older adults
  • People with limited sun exposure
  • People with darker skin tones
  • People who are obese or overweight
  • Those with gastrointestinal disorders like celiac disease, IBD, or absorption issues
  • Osteoporosis patients
  • Pregnant and breastfeeding women

Consult your healthcare provider to determine if you need a vitamin D supplement or increased sun exposure.

The takeaway

Vitamin D is a crucial nutrient that many people don’t get enough of from diet and sun exposure alone. Excellent food sources include fatty fish, fish liver oils, egg yolks, UV-treated mushrooms, and fortified foods.

Moderate sun exposure can satisfy needs during warmer months, especially for lighter-skinned people. However, many need supplements to maintain optimal blood levels year round.

Since vitamin D deficiency is common yet often asymptomatic, get your levels tested to determine if you need more from dietary sources, sunlight, or supplementation.