Vitamin D is also known as the sunshine vitamin – what are the health benefits of vitamin D, what is the function of vitamin D, and how much do you need?
What is vitamin D?
Vitamin D is often referred to as the sunshine vitamin because of the way it can be made by the body when your skin is exposed to the sun. It is an essential, fat-soluble vitamin, which means that it can be stored in the body for extended periods and it is not excreted out of the body like a water-soluble vitamin. Vitamin D also has two forms: vitamin D2 and vitamin D3.
Where is vitamin D found?
Vitamin D3 is made by the body with exposure to UVB radiation from the sun. This inactive vitamin D3 is then converted to 1,25-dihydroxyvitamin D (1,25(OH)2D), which is the active form of vitamin D, by the liver and kidneys. UVB radiation is significantly reduced on cloudy days and it does not penetrate through windows. Small amounts of UVB can still be absorbed when wearing a sunscreen with sun protection factor (SPF).
There are also some food sources of vitamin D. Vitamin D3 is naturally found in small amounts in cheese and egg yolks, and in larger amounts in fish liver oils and fatty fish including salmon, tuna, or mackerel. Vitamin D2 can be inconsistently found in some mushrooms that have been exposed to sunlight.
Fortified foods are a good source of vitamin D; these foods include milk and fortified kinds of plant-based milk alternatives, orange juice, margarine, cereals, and yogurt. Make sure to check the label, as not all kinds of these products are fortified with vitamin D. Some people may find it helpful to take a vitamin D supplement to ensure they meet their recommended vitamin D intake.
Why is vitamin D important?
Vitamin D and calcium work together to maintain bone health. Vitamin D increases calcium absorption from food and assists bone cells (called osteoblasts and osteoclasts) in maintaining the strength and size of bones.
Another function of vitamin D is regulating cell growth, as vitamin D regulates the production of proteins that help cell division and apoptosis (controlled cell death).
Vitamin D plays a role in the innate immune system, which helps keep pathogens out of the body and prevent infection.
What is the RDA for vitamin D?
The Recommended Dietary Allowance (RDA) for vitamin D is 600 IU, or 15 micrograms (mcg) for all individuals between 1 and 70 years of age, including pregnant and lactating women. The RDA for infants under twelve months is 400IU, or 10mcg, and the RDA for seniors over 70 years of age is 800IU, or 20mcg.
It is important to note that breastfed infants cannot meet their RDA of vitamin D through breast milk alone, and it is important to supplement breastfed infants with a daily supplement containing 400IU of vitamin D.
These values are given by the National Institutes of Health, and the RDA represents the daily intake sufficient to meet the dietary needs of 97-98% of healthy individuals. One tablespoon of cod liver oil provides 170% of the daily RDA, and milk or fortified plant-based milk alternatives usually contain 13-18% of the daily RDA per serving. Getting between five and 30 minutes of sun exposure twice a week without sunscreen on the face, arms, legs, or torso can also help reach the RDA of vitamin D.
How much is too much?
Since vitamin D is a fat-soluble vitamin, toxicity is possible as it is not easily excreted from the body like a water-soluble vitamin. The Upper Limit (UL) given by the National Institutes of Health is 4,000IU for people aged nine and above. The UL of vitamin D is 3,000IU for children between four and eight years of age, 2,500IU for children between one and three years, 1,500IU for infants between seven and twelve months, and 1,000IU for infants under six months of age.
It is important to note that vitamin D toxicity can only occur from excess vitamin D consumption from food and supplements, not from excessive sun exposure. Prolonged vitamin D intake significantly above the UL might lead to an increased risk of some adverse health effects. For example, an extreme excess of vitamin D can raise blood calcium levels through increased calcium absorption. Elevated blood calcium levels can damage the cardiovascular system and kidneys by promoting calcification of the tissues, and it is associated with an increased risk of kidney stones. In addition, vitamin D toxicity can have a variety of side effects including unexplained weight loss and cardiac arrhythmias.
What are the benefits of vitamin D?
Some evidence suggests that vitamin D can have certain health benefits. For example, adequate vitamin D consumption could potentially protect against osteoporosis by increasing calcium absorption. One review found that supplementing calcium and vitamin D together was associated with slight beneficial outcomes for bone mineral density compared with a placebo.
In addition, some research suggests that vitamin D could help protect against some cancers. One study of over 3,000 adults that had a colonoscopy found that those with the highest vitamin D intakes had a decreased risk of cancerous lesions in the colon.
Vitamin D deficiency
It can be difficult to consume enough vitamin D through food, and not everyone has access to fortified foods, supplements, and continuous sun exposure. Some groups are more susceptible to vitamin D deficiency than others.
People who do not get a lot of sun exposure are at an increased risk of vitamin D deficiency since they are not getting much of it through sunlight. People with darker skin are also at a higher risk because the increased melanin pigment in their skin reduces their ability to produce vitamin D from the sun.
Older adults are also at risk of deficiency for two primary reasons. First, they tend to spend more time indoors, which reduces their sun exposure. Next, skin loses its ability to produce vitamin D as efficiently with age.
Individuals with obesity may have an increased risk of vitamin D deficiency because higher amounts of subcutaneous fat can impact the circulation of vitamin D in the body.
Finally, those with conditions that impact fat absorption, such as cystic fibrosis, Crohn’s disease, and celiac disease, are at risk of deficiency.
Vitamin D deficiency can potentially result in adverse health effects. Rickets results from vitamin D deficiency in children, and it is characterized by soft and brittle bones. Osteomalacia can be a result of vitamin D deficiency in adults, and it is often characterized by weak bones, bone pain, and muscle weakness.
Vitamin D Supplementation
Vitamin D deficiency can fortunately be easily treated with vitamin D supplementation to raise vitamin D levels. Standard treatment for rickets includes vitamin D supplementation and potentially surgery to correct any related bone deformities. Osteomalacia is also treated through vitamin D supplementation.
If you think you are deficient in vitamin D or are at risk for deficiency, consider getting your blood levels tested. As always, consult your doctor before you begin taking any vitamin or mineral supplement, to make sure your medications or health conditions don’t make it a serious risk.
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