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Vitamin D (Secosteroids)

Vitamin D is a group of fat-soluble vitamins that help the body absorb and regulate minerals such as calcium and phosphorus. In reality, vitamin D acts more like a hormone in the body and is essential for keeping bones strong and healthy.

The most important and notable D vitamins are vitamin D2, also known as cholecalciferol, and vitamin D3, or ergocalciferol. Vitamin D3 is produced by the skin when exposed to sunlight. D2, on the other hand, is produced naturally by plants, yeast and fungi and is also a synthetic form found in supplements and fortified foods. Both forms have been found to be effective at raising levels of vitamin D in the blood.

Sources of Vitamin D

Sun exposure is the primary source of vitamin D, other than supplements. Factors including the season, time of day, weather conditions, skin melanin content, and sunscreen use affect vitamin D synthesis via UV radiation exposure.

There are, however, a handful of food sources that can be added to a well-balanced diet to help increase vitamin D intake, such as:

  • Fatty fish, especially salmon, tuna, and mackerel
  • Fish liver oils, such as cod liver oil
  • Beef liver, which can include freeze-dried beef liver supplements
  • Alfalfa herb
  • Cheese
  • Egg yolks
  • Select mushrooms and enhanced mushrooms exposed to controlled levels of UV light
  • Fortified foods such as milk, certain cereals and yogurts, and specific brands of orange juice

Vitamin D Nutrition Information

Vitamin D helps the gut absorb calcium and regulates serum calcium and phosphate, thus enabling bone mineralization. Vitamin D is also essential for bone growth and restructuring by osteoblasts and osteoclasts. Without enough vitamin D, bones may become brittle or misshapen or lead to rickets in children or osteoporosis in adults.

Vitamin D Deficiency

Since vitamin D is found in so few foods, and because of a lack of sun exposure due in part to more time spent indoors and increased sunscreen use, many people don’t get the amount of vitamin D their bodies need. In fact, three out of four Americans are vitamin D deficient. Causes of vitamin D deficiency include:

  • Inadequate daily intake
  • Limited sun exposure
  • Kidneys are unable to convert Vitamin D into its active form
  • Poor absorption in the digestive tract
  • Milk allergies
  • Restrictive diets such as ovo-vegetarianism and veganism

Insufficient vitamin D levels have been associated with illnesses such as:

  • Heart disease
  • Diabetes
  • Rickets
  • Osteomalacia
  • Mental illness such as depression
  • Osteoporosis
  • Autoimmune disease
  • Cancer

Medical Uses of Vitamin D

Vitamin D has been used in treatments against a variety of medical conditions.

Cancer: While it is still being researched, several studies have shown that adequate to higher blood levels of vitamin D are associated with a reduced risk of certain cancers, such as colorectal cancer. However, further studies are needed to determine vitamin D’s efficacy as a treatment or prevention option. It is also best to try to increase vitamin D intake through food rather than sun exposure to avoid an increased risk of developing melanoma.

Depression: There is some evidence that suggests that insufficient levels of vitamin D can lead to feelings of depression.

HIV: Vitamin D deficiency and insufficiency are common in people with HIV, but it has been found that it is possible to raise their vitamin D blood levels with supervised supplementation. This is an important finding because it has also been suggested that vitamin D can slow the progression of HIV and AIDS. Vitamin D also supports the immune system in a variety of ways.

Skin disorders: Many people also find vitamin D helpful in treating skin conditions including vitiligo, scleroderma, psoriasis, actinic keratosis, and lupus vulgaris.

Recommended Daily Intake

Recommended daily allowances are as follows:

  • Infants — 10 micrograms (μg) per day (400 IU).
  • Men and women:
    • Between 1 and 70 years old — 15 micrograms (μg) per day (600 IU).
    • 71 years or older — 20 micrograms (μg) per day (800 IU).
  • Women who are pregnant or breastfeeding — 15 micrograms (μg) per day (600 IU).

Vitamin D Toxicity

While it is highly unlikely, it is possible to have an excessive intake of any nutrient, including vitamin D. Toxic levels of vitamin D for adults and children older than 8 years old is anything more than 100 μg per day (4000 IU). Toxicity is most often caused by dietary supplementation rather than from food or sun exposure. While the sun cannot cause vitamin D toxicity, it’s still important to limit sun exposure and use sunscreen to reduce the risk of skin cancer.

Toxic effects of Vitamin D include:

  • Calcinosis, or the deposit of calcium salts in organ tissues such as the kidneys, heart, and lungs
  • Hypercalcemia, or high calcium blood levels

*This page is for informational purposes only and shouldn't replace medical advice.

Try some Vitamin D-Rich Foods!