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Vitamin D is a fat-soluble vitamin produced in the skin when it is exposed to sunlight. Vitamin D is also naturally occurring in certain foods such as fatty fish, cod liver oil, and eggs.
Vitamin D helps the body absorb dietary calcium and phosphorus from the intestines and suppresses the release of parathyroid hormone, a hormone that causes bone resorption. This helps keep bones healthy. Vitamin D is also believed to improve muscle and immune function.
21 food sources of Vitamin D
Foods that are highest in vitamin D include:
- Oily fish
- Herring
- Mackerel
- Salmon
- Sardines
- Swordfish
- Trout
- Tuna
- Meat and poultry
- Vegetables
- Mushrooms — white button, shiitake, oyster, and portabella
- Dairy products
- Cheddar cheese
- Milk, vitamin D fortified
- Yogurt, vitamin D fortified
- Other
- Cod liver oil
- Egg yolk
- Orange juice, vitamin D fortified
- Plant-based milk (e.g., soy, almond, oat), vitamin D fortified
- Ready-to-eat breakfast cereals, vitamin D fortified
What Does Vitamin D Do in the Body?
In the body, vitamin D assists with the following functions:
- Bone health and reduced risk of osteoporosis
- Strengthens muscles
- Helps with immune system function
- Reduces inflammation
- Aids in glucose (sugar) metabolism which may help prevent diabetes
- Helps promote heart health and lowers the risk of cardiovascular disease
- Lowers the risk of tooth decay and gum disease
What Is Vitamin D Deficiency?
Vitamin D deficiency is another term for low levels of vitamin D.
Symptoms of low vitamin D include:
- Bone problems
- Muscle aches or cramps
- Muscle spasms
- Muscle weakness
- Fatigue
- Cognitive impairment in older adults
- Severe asthma in children
- Cancer
What Causes Low Vitamin D?
Low vitamin D (vitamin D deficiency) may be caused by:
- Low levels of vitamin D in the diet combined with inadequate sun exposure
- Some medical conditions that result in an inability to absorb vitamin D from the intestines
- Celiac disease
- Crohn's disease
- Cystic fibrosis
- Surgery that removes or bypasses portions of the stomach or intestines such as gastric bypass
- An inability to process vitamin D due to kidney or liver disease
- Certain medications
- Anti-seizure medications
- Cholesterol-lowering drugs
- Laxatives
- Steroids
- Tuberculosis medication
- Weight loss medications
- Other factors
- Wearing clothes that cover most of the skin when outdoors
- Having dark skin, because people with dark skin may not produce sufficient vitamin D from sunlight
- Obesity
- Living in institutions such as nursing homes
- Not going outside often, such as people who are ill or housebound
What Is the Treatment for Low Vitamin D?
In addition to consuming foods that are good sources of vitamin D, treatment for low vitamin D (vitamin D deficiency) may also include:
- Vitamin D supplements
- Cholecalciferol (vitamin D3)
- This form of vitamin D is usually recommended because it is the naturally occurring form of the vitamin and it may raise vitamin D levels more effectively
- Ergocalciferol (vitamin D2)
- Cholecalciferol (vitamin D3)
- Additional supplements
- Calcium
- 1000 mg of calcium per day for premenopausal women and men
- 1200 mg per day for postmenopausal women
- Calcium
Exposure to sunlight is a source of vitamin D but excess sun exposure can cause sunburn, premature skin aging, eye damage, heat exhaustion or heat stroke, or skin cancer. Sun exposure is not recommended as a source of vitamin D for infants and children because of the potential risks of skin cancer. Talk to your doctor about how much sun exposure you may need and how to do so safely.
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https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
https://www.uptodate.com/contents/vitamin-d-deficiency-beyond-the-basics?search=vitamin%20d%20deficiency&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2
https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
https://www.merckmanuals.com/home/disorders-of-nutrition/vitamins/vitamin-d-deficiency
https://www.hsph.harvard.edu/nutritionsource/vitamin-d/