What is vitamin D?
Benefits of vitamin D include helping the body absorb calcium and supporting the immune system.
Vitamin D is a nutrient that is important for health. Certain foods contain a small amount, but people can make most of the vitamin D that they need from sunlight.
Some of the benefits of vitamin D include:
- helping the body to absorb calcium for strong bones
- supporting nerves to carry messages to and from the brain
- playing a part in muscle movement
- supporting the immune system to fight infection and disease
Vitamin D is different from most other vitamins. When the body processes it, vitamin D becomes a hormone called calcitriol, which makes bones in the body absorb calcium.
Can you get enough vitamin D from the sun alone?
Some people will be able to get enough vitamin D just from sunlight. However, it depends on where in the world they live, the time of year, the time of day, and their skin color.
People who live nearer the equator get more sun exposure. In the Northern Hemisphere, a person may not get sufficient vitamin D from sunlight during the winter.
The sun is usually strongest between 11:00 a.m. and 3:00 p.m. In the summer, a person does not need to be out in the sun for very long during this period to make enough vitamin D.
The amount of melanin a person’s skin contains affects how much vitamin D they can make. Less melanin results in lighter skin, which does not protect as well against harmful ultraviolet (UV) rays.
People with more melanin in their skin have better protection from the sun, but take longer to make vitamin D. In the United States, the Centers for Disease Control and Prevention (CDC) found that Mexican-Americans and non-Hispanic black people are more likely to have vitamin D deficiency.
These varied factors make it difficult to recommend how much sunlight a person should get to make the vitamin D that their body needs.
The Vitamin D Council gives some examples:
- At noon during summer in Miami, someone with a medium skin tone would need to expose one-quarter of their skin to sunlight for 6 minutes.
- At noon during summer in Boston, someone with a darker skin tone would need to expose one-quarter of their skin to sunlight for 2 hours.
Some people may not absorb enough vitamin D from sunlight because of specific lifestyle factors. For example, individuals who work at night, stay indoors during daylight hours, always cover their skin, or use a high-factor sunscreen every day.
The body can only make a certain amount of vitamin D at once. After this, it is vital to protect the skin from UV rays. UV rays can cause burning, aging of the skin, and increase a person’s risk of skin cancer.
What is the medical definition of vitamin D deficiency?
Scientists use nanograms per milliliter (ng/mL) to measure the level of vitamin D in the blood. There is currently no set level for vitamin D deficiency.
Some experts classify deficiency as having less than 12 ng/mL of vitamin D in the blood, and state that levels below 20 ng/mL are too low for healthy bones and general wellbeing. However, othersbelieve that the level should be higher, and classify deficiency as anything less than 30 ng/mL.
Vitamin D deficiency over a lifetime can cause osteoporosis.
Vitamin D deficiency in children can cause rickets. This is a condition that makes bones soft, causing them to bend. A deficiency can also cause bone pain and weak muscles in adults.
Not having enough vitamin D or calcium over a lifetime may contribute to osteoporosis. This causes fragile bones that may fracture more easily.
There may be a connection between vitamin D and other medical problems and diseases, but more research is necessary to confirm this.
Recommended daily intake
The recommended dietary intake for vitamin D is difficult to judge, as it is dependent on sun exposure. This varies from person to person according to where they live and the time of year, among other factors.
For this reason, guidelines base their recommended intakes on the assumption that a person gets minimal sun.
The recommended dietary intake is in IU, which is International Units. The Food and Nutrition Board (FNB) recommend the following intake per day to maintain a healthy level of vitamin D:
|Age||Recommended daily intake of vitamin D|
|0 to 12 months||400 IU|
|1 to 70 years||600 IU|
|70 years and above||800 IU|
For adults with vitamin D levels below 30 ng/mL, the Endocrine Society guidelines recommend a daily intake of 1,500–2,000 IU to restore healthy levels of vitamin D. There are also treatment options where people with vitamin D deficiency receive 50,000 IU weekly or monthly instead of taking a daily dose.
Good sources of vitamin D
Cheese is a natural source of vitamin D.
Natural sources of vitamin D include:
- egg yolk
- beef liver
Many foods in the U.S. are fortified, meaning that the manufacturers add vitamins to them. Breakfast cereals, milk, and orange juice often contain added vitamin D. The nutrition label should make it clear when this is the case.
Breast-fed babies and young children will often need a vitamin D supplement. This is because breast milk does not give a baby all of the vitamin D that they need. Vitamin D drops are available over-the-counter (OTC).
Babies and young children who have formula, which contains added vitamin D, should not need supplements.
There are two forms of Vitamin D found in supplements and fortified foods:
- vitamin D2, or ergocalciferol
- vitamin D3, or cholecalciferol
These two forms are generally equivalent, and both raise a person’s vitamin D levels effectively. However, at higher doses, vitamin D2 is less potent.
Can you take too much vitamin D?
Too much vitamin D can be harmful. It is not possible for the body to make too much vitamin D from sun exposure.
Having too much in the body usually results from taking supplements. However, it is very rare and usually only occurs when people take a very high dose for an extended period, such as more than a year.
The maximum quantity of vitamin D that a person can take before it causes health problems is 4,000 IU daily. Symptoms of having too much vitamin D in the blood include:
- loss of appetite
- weight loss
- kidney damage
Taking too much vitamin D can raise the level of calcium in the blood. This can cause health problems such as mental confusion and heart problems.
People who are taking specific medication should not take a vitamin D supplement. This is because it can interact with these medicines and stop them from working. Examples include some corticosteroids, weight-loss drugs, and medication for epilepsy.
When to see a doctor
If a person is concerned that they may have a vitamin D deficiency, a doctor can arrange for a blood test to measure their vitamin D levels.
Many people get enough vitamin D from sunlight and fortified foods. A person who lives in the Northern Hemisphere may choose to take a supplement during the winter months.
If a person has taken too much vitamin D in supplement form, they may have symptoms of vitamin D toxicity. Seeking medical advice can help to safeguard long-term health.