Vitamin D—everything you need to know about it
Vitamin D is completely different from most other vitamins. In fact, it is a so-called prohormone that is produced from cholesterol when your skin is exposed to sunlight. For this reason, vitamin D is often called the “sunshine vitamin.”
However, sun exposure rarely provides sufficient vitamin D, so we need to obtain it from supplements or our diet. Yet only a few foods contain significant amounts of this vital vitamin, and deficiency is very common. In fact, approximately 41.6% of the U.S. population is deficient. This article explains everything you need to know about vitamin D.
What is vitamin D?
Vitamin D is a fat-soluble vitamin, meaning that it dissolves in fat and oil and can be stored in the body for a long time.
There are two main dietary forms:
- Vitamin D3 (cholecalciferol). It is found in some animal-derived foods, such as fatty fish and egg yolks.
- Vitamin D2 (ergocalciferol). It is found in some plants, mushrooms, and yeasts.
Of the two, D3 (cholecalciferol) appears to be almost twice as effective at increasing blood vitamin D levels as D2 (ergocalciferol).
SUMMARY Vitamin D is a fat-soluble vitamin that the body can store for a long time. Of its two main forms—D2 and D3—the latter is more effective at raising vitamin D levels in the blood.
What does it do in the body?
Vitamin D must undergo two conversion steps to become active.
First, it is converted in the liver into calcidiol, or 25(OH)D. This is the vitamin’s storage form.
Second, it is converted into calcitriol, or 1,25(OH)2D, mainly in the kidneys. This is the active steroid hormone form of vitamin D. Calcitriol interacts with the vitamin D receptor (VDR), which is found in virtually every cell in the body.
When the active form of vitamin D binds to this receptor, it switches genes on or off, leading to changes in your cells. This works similarly to most other steroid hormones.
Vitamin D affects various cells involved in bone health. For example, it promotes the absorption of calcium and phosphorus from the intestines. However, scientists have recently discovered that it also plays a role in other areas of health, such as immune system function.
SUMMARY Vitamin D is converted into calcidiol, the storage form of the vitamin, which is then converted into calcitriol, the active steroid form. Calcitriol binds to the vitamin D receptor in our cells, switching genes on or off.
Sunlight is an effective way to obtain vitamin D
Vitamin D can be produced from cholesterol in the skin when it is exposed to the sun’s ultraviolet B (UVB) rays.
If you live in an area with abundant sunshine, you can probably obtain all the vitamin D you need by getting some sun a few times a week. Keep in mind that you need to expose most of your body. If you expose only your face and hands, you will produce much less vitamin D. Also, if you stay behind glass or use sunscreen, you will produce less vitamin D—or none at all.
However, be sure to use sunscreen if you stay in the sun for an extended period. Sunlight is healthy, but sunburn causes premature skin aging.
If you stay in the sun for an extended period, consider remaining without sunscreen for the first 10–30 minutes—depending on your sensitivity to sunlight—and then apply it before you begin to burn.
Because vitamin D is stored in the body for weeks or months, you may need sunlight only occasionally to keep your blood levels adequate.
Nevertheless, if you live in an area without adequate sunlight, obtaining vitamin D from food or supplements is essential—especially during winter.
SUMMARY Sunlight is an effective way to obtain vitamin D, but sunscreen inhibits its production. Although safe sun exposure can help achieve adequate levels, many people do not have access to sunlight for much of the year.
Best food sources
Here are some of the best food sources of vitamin D3:
- Cod liver oil, 1 tablespoon (15 ml) 1,360 IU / 34 mcg
- Salmon, cooked, 3 ounces (85 grams) 447 IU / 11 mcg
- Tuna, canned in water, 3 ounces (85 grams) 154 IU / 4 mcg
- Beef liver, cooked, 3 ounces (85 grams) 42 IU / 1 mcg 42 IU / 1 mcg
- 1 large whole egg (the D is in the yolk) 41 IU / 1 mcg
- 1 sardine, canned in oil, drained 23 IU / 0.6 mcg
Although fatty fish such as salmon, mackerel, swordfish, trout, tuna, and sardines are good sources, you would need to eat them almost every day to get enough.
The only excellent dietary source of vitamin D is fish liver oil—such as cod liver oil—which contains more than twice the reference daily intake (RDI) in a single tablespoon (15 ml). Keep in mind that dairy products and grains are often fortified with vitamin D. Some rare mushrooms also contain vitamin D, and egg yolks contain small amounts.
SUMMARY Cod liver oil is the single best source of vitamin D3. Fatty fish are also a good source, but they must be eaten frequently to obtain enough.
Symptoms of deficiency
Vitamin D deficiency is one of the most common nutrient deficiencies.
Some people are at greater risk than others. In the United States, 41.6% of the total population is vitamin D deficient, although minorities fare worse—82.1% of Black people and 69.2% of Hispanic people are vitamin deficient.
In addition, older adults have a much higher risk of deficiency. People with certain diseases are also very likely to be deficient. One study found that 96% of people who had experienced a heart attack had low vitamin D levels.
Overall, vitamin D deficiency is a silent epidemic. Symptoms are usually subtle, and it can take years or decades for them to appear.
The best-known symptom of vitamin D deficiency is rickets, a bone disease common among children in developing countries.
Rickets has largely disappeared from Western countries because some foods have been fortified with vitamin D.
Deficiency is also associated with osteoporosis, reduced mineral density, and an increased risk of falls and fractures in older adults.
Moreover, studies suggest that people with low vitamin D levels have a much higher risk of heart disease, diabetes (type 1 and type 2), dementia, and autoimmune diseases such as multiple sclerosis.
Finally, vitamin D deficiency is associated with a reduced life expectancy. Nevertheless, it is unclear whether the deficiency contributes to these diseases or whether people with low levels are simply more likely to develop them.
SUMMARY Vitamin D deficiency is associated with several health problems and a reduced life expectancy.
Potential health benefits
Here are some potential benefits of vitamin D:
- Reduces the risk of osteoporosis, falls, and fractures. Higher doses of vitamin D may help prevent osteoporosis, falls, and fractures in older adults.
- Better physical fitness. Vitamin D may increase physical strength in both the upper and lower limbs.
- Treating depression. Studies suggest that vitamin D may alleviate symptoms in people with clinical depression.
- Reduces the risk of type 1 diabetes. A study in infants found that daily intake of 2,000 IU of vitamin D reduced the risk of type 1 diabetes by 78%.
SUMMARYResearch suggests that vitamin D may have several benefits related to bone health, mental health, and autoimmune diseases. However, more studies are needed.
How much should you take?
The only way to find out whether you are deficient—and therefore whether you need supplementation—is to have your blood level measured.
Your healthcare provider will measure the storage form of vitamin D, called calcifediol. Any level below 12 ng/mL is considered deficient, while any level above 20 ng/mL is considered adequate.
The RDI for vitamin D is as follows:
- 400 IU (10 mcg): infants, ages 0–12 months.
- 600 IU (15 mcg): children and adults, ages 1–70.
- 800 IU (20 mcg): older adults and pregnant or breastfeeding women.
Although an adequate level is measured at 20 ng/mL, many health experts believe that people should aim for blood levels above 30 ng/mL for optimal health and disease prevention.
In addition, many people believe that the recommended intake is too low and that people need much more to achieve optimal blood levels.
According to the U.S. National Academy of Medicine, the safe upper limit is 4,000 IU (100 mcg) per day.
Vitamin D3 supplements appear to be more effective at raising vitamin D levels than D2 supplements. D3 capsules are available at most supermarkets and health food stores, as well as online.
SUMMARY The RDI for vitamin D is 400 IU (10 mcg) for infants, 600 IU (15 mcg) for children and adults, and 800 IU (20 mcg) for older adults and pregnant or breastfeeding women.
Optimize your other nutrients
It is important to note that nutrients generally do not work in isolation.
They often depend on one another, and increased intake of one nutrient may increase the need for another.
Some researchers believe that fat-soluble vitamins work together, and that ensuring optimal intake of vitamins A and K is crucial when supplementing with vitamin D3.
This may be particularly important for vitamin K2, another fat-soluble vitamin that most people do not get enough of. Magnesium, another important mineral that is often lacking in the modern diet, may also be important for vitamin D function.
SUMMARY Evidence suggests that vitamin D works together with magnesium and vitamins A and K to promote health.
What happens if you take too much?
It is a myth that vitamin D can easily be overdosed. Vitamin D toxicity is very rare and only occurs when you take very high doses for a long time. The main symptoms of toxicity include confusion, lack of concentration, drowsiness, depression, nausea, abdominal pain, constipation, and high blood pressure.
SUMMARY Vitamin D toxicity is very rare. Symptoms include confusion, drowsiness, depression, constipation, and high blood pressure.
Vitamin D is a fat-soluble vitamin that is important for bone health.
For those who have low levels of this nutrient, increasing intake may reduce depression and improve physical strength.
Your skin produces vitamin D when exposed to sunlight. Foods such as fatty fish, fish oil, liver, and some artificially fortified foods and supplements also contain vitamin D.
The deficiency is relatively common because exposure to sunlight is limited and there are few rich dietary sources. If you spend little time in the sun and rarely eat fatty fish, consider supplementation. Getting enough vitamin D can go a long way toward improving your health.
Source: www.healthline.com
