There is no doubt that our bodies need vitamin D. It helps regulate the absorption of calcium and phosphorus in our bones, helps our cells to communicate with each other, and helps strengthen our immune system. But can vitamin D supplementation really offer additional health benefits?
Previous research suggests it can. But other studies indicate that vitamin D supplementation does not do any more than promote bone and immune system health and is only useful for people who have a vitamin D deficiency.
We look at both sides of the argument in an attempt to determine whether vitamin D supplementation really is good for us.
How vitamin D works
Vitamin D is a fat-soluble vitamin. There are five forms of the vitamin - D1, D2, D3, D4 and D5.
However, vitamins D2 and D3 appear to be the most important in the human body.
Sunlight is the the body's main source of vitamin D. There is no set amount of time a person should spend in the sunlight to get a good amount of this vitamin. However, the Vitamin D Council state that "you don't need to tan or burn your skin to get vitamin D."
The UK's National Health Service (NHS) states that short bursts of sun exposure during summer months should be enough.
The energy from the sun changes a chemical in the skin to vitamin D3, which is then carried to the liver and the kidneys where it is made into active vitamin D.
Some foods, such as oily fish, eggs and fortified fat spreads, also contain the vitamin, although these are in very small amounts. Once consumed, it is sent to the liver and processed in the same way.
The main function of vitamin D is to increase the intestinal absorption of calcium - a process that is crucial for good bone health.
Vitamin D also helps strengthen the immune system and aids cell to cell communication in the body.
The Vitamin D Council also state that the vitamin is important for muscle function, the respiratory system, cardiovascular function, brain development, and it even has anti-cancer properties.
Vitamin D deficiency
Vitamin D deficiency occurs when a person does not have the sufficient amount of the vitamin in their body.
According to the Food and Nutrition Board at the Institute of Medicine of The National Academies, the recommended dietary allowance of vitamin D for people aged 1-70 is 600 IU each day and 800 IU for those aged over 70 years.
Infants between 0-12 months should have an intake of 400 IU of vitamin D each day.
The NHS state that the majority of people should be able to get all the vitamin D the body needs by eating a healthy balanced diet and getting the right amount of sunlight.
But certain groups may be at risk of vitamin D deficiency. These include:
- People aged 65 and over
- Pregnant and breastfeeding women
- Individuals who are not exposed to enough sunlight, such as people who are housebound
- People who have darker skin, and
- Babies and young children under the age of 5.
According to Harvard Medical School, if the body does not get enough vitamin D, it can only absorb 10-15% of dietary calcium, compared with 30-40% with sufficient vitamin D levels.
This can have negative impacts on bone health. Last year, Medical News Today reported on a study revealing that vitamin D deficiency may speed up the aging of bones.
Low vitamin D levels have also been linked to other negative health effects. A recent study suggested that vitamin D deficiency may cause damage to the brain.
Research has also revealed potential implications for vitamin D deficiency during pregnancy. A study recently suggesting that women who have low vitamin D levels in the first 26 weeks of gestation may have an increased risk of preeclampsia.
According to the Vitamin D Council, symptoms of vitamin D deficiency can include tiredness and general aches and pains, but many people do not have any symptoms.
Potential benefits of vitamin D supplementation
The Vitamin D Council state that the two main ways to get sufficient amounts of vitamin D in the body are to expose bare skin to sunlight and take vitamin D supplements.
But Brant Cebulla, development director of the Vitamin D Council, told Medical News Today that for many people, frequent exposure to sunlight is not possible:
"With our indoor lifestyles, we don't expose skin to the sun as much as we used to and are not fulfilling our vitamin D requirements. Supplements are one way to make up for this lifestyle."
Vitamin D supplementation has been linked to numerous health benefits.
More recent research has suggested that high levels of vitamin D may prevent cognitive impairment in patients with Parkinson's disease, while another study found that high vitamin D intake during pregnancy may increase the muscle strength of offspring.
Health benefits challenged
However, some studies have questioned the potential health benefits of vitamin D supplementation.
Last year, a study published in The Lancet Diabetes & Endocrinology that analyzed 290 prospective observational studies and 172 randomized trials of vitamin D supplements, found no evidence that vitamin D supplementation yields any health benefits.
Furthermore, the study researchers suggested that low vitamin D levels are a consequence of ill health, not a cause.
A more recent study, also published in The Lancet Diabetes & Endocrinologyquestioned the health benefits of vitamin D supplementation.
The research team, led by Dr. Mark Bolland of the University of Auckland in New Zealand, found that vitamin D supplementation is unlikely to reduce the incidence of heart attack, heart disease, stroke, cancer or bone fractures.
Talking to Medical News Today, Dr. Bolland said of the team's findings:
"The main message is that if you are otherwise healthy and active, you are likely to receive enough sunshine to have adequate vitamin D levels and don't need to take vitamin D supplements."
However, Cebulla noted that studies such as these may not be showing the true effects of vitamin D supplementation:
"These meta-analyses pulled lots of data from trials that used really low amounts of vitamin D (400 or 800 IU a day), so it's hard to expect results that show any benefits."
He added that future studies should provide more accurate results:
"We've got better designed large trials underway now, using 2,000 IU of vitamin D a day or more, and results from those will be out in 2017-2020. One such trial is VITAL, which is enrolling 20,000 Americans to take either 2,000 IU of vitamin D or placebo for 5 years. We should get really good data from that, data that doesn't exist to date."
Negative effects of vitamin D supplementation
Like many other vitamins, excess intake of vitamin D can pose negative health effects.According to the University of Maryland Medical Center, side effects can include poor appetite, weight loss, tiredness, sore eyes, vomiting, diarrhea and muscle problems.
"If you have extremely high levels of vitamin D, you could get a condition called hypercalcemia, which means too much calcium in your blood," added Cebulla.
"This condition makes you feel nauseous, confused and tired. If you get medical attention and lower your vitamin D intake and lower your calcium levels, there are no long lasting effects."
The University of Maryland Medical Center states that it is hard to get too much vitamin D from sunlight and food sources, therefore excess vitamin D intake is generally a result of taking too many supplements.
However, it is difficult to say how much is too much because most organizations recommend different maximum intakes of vitamin D.
For example, the Food and Nutrition Board recommend that 4,000 IU is the maximum amount of vitamin D that should be taken each day, while the Vitamin D Council recommend 10,000 IU as the maximum.
However, the Vitamin D Council note:
"While these amounts seem like a lot, keep in mind that your body can produce 10,000 to 25,000 IUs of vitamin D after a little bit of full body sun exposure. Vitamin D toxicity, where vitamin D can be harmful, usually happens if you take 40,000 IU a day for a couple of months or longer."
Increased awareness surrounding vitamin D
Cebulla told Medical News Today that in order to ensure individuals are getting the right amounts of vitamin D, doctors should be discussing vitamin D intake with their patients:
"Studies show that traditional dietary counseling do not improve vitamin D intake/levels. So it's important for doctors to make sure they communicate that vitamin D isn't something that comes from your diet, and extra attention is needed to make sure you're getting enough vitamin D."
Furthermore, Cebulla added that increased awareness surrounding vitamin D would lead to better vitamin D intake over the population.
"We need a population that understands you get vitamin D from sun exposure, and if you're not getting sun exposure, then you need to supplement because you're not getting enough vitamin D from your diet," he said.
For now, evidence suggests that vitamin D supplements may help to maintain the levels of the vitamin our bodies need to promote bone health, modulation of cell growth and immune function.
But whether these supplements can promote additional health benefits remains to be seen.