Everything You Need to Know About Vitamin D

By Aja Webber – September 1, 2021

Vitamin D is an essential ingredient needed for our bodies to function properly. You probably already know that you can get it from the sun, citrus fruits and supplements, but what does vitamin D actually do within our bodies? Sure, it can help support the immune system when you’re sick, but there are plenty of other benefits of this vitamin for the body.

What is Vitamin D?

Calciferol — more commonly known as vitamin D — is a fat-soluble prohormone that can be found in certain foods and is available as a dietary supplement. Another source of vitamin D is the infamous sun. When ultraviolet rays from sunlight make contact with skin, it triggers a reaction called vitamin D synthesis and allows your body to absorb vitamin D from the sun.

Despite its name, vitamin D is not actually a vitamin. Shocking, right? Vitamins are not naturally produced by the body, but must be absorbed through supplementation. Vitamin D, however, is naturally occurring in the body, and therefore it is known as a prohormone which is the precursor of a hormone.

While vitamin D is naturally occurring, some can suffer from a vitamin D deficiency for a variety of reasons. Here we will dive into the many factors that can contribute to vitamin D deficiency.

Vitamin D Deficiency

There are six main factors that can increase your risk of developing a vitamin D deficiency.

  1. Diet
  2. Exposure to sunlight
  3. Skin tone
  4. Kidney function
  5. Digestive tract problems
  6. Obesity

Natural sources of vitamin D typically come from animal products such as eggs, fish, milk and liver. Therefore, someone on a strictly vegan diet may be more susceptible to vitamin D deficiency.

Spending time outside in the sunlight is a great way to prevent a vitamin D deficiency, because your body is able to produce more vitamin D when your skin is exposed to sunlight via vitamin D synthesis. If you have darker skin, you may be less likely to get sufficient amounts of vitamin D from sunlight due to higher amounts of melanin.

Poor kidney function may also affect your body’s ability to convert vitamin D into its active form. The same goes for digestion issues —  Crohn’s disease, cystic fibrosis and celiac disease can all negatively impact your intestines’ ability to absorb vitamin D from the food you eat.

Studies have shown that having a body mass index greater than 30 is associated with lower vitamin D levels. Vitamin D is a fat soluble prohormone, so an excess of fat cells in the body keeps vitamin D isolated, preventing it from being released. Therefore obesity often makes it necessary to take larger doses of vitamin D supplements in order to reach and maintain healthy levels.

Jesse O’Brien studies fitness as it relates to nutrition and is the owner and head coach of Central Athlete, a gym and training center in Austin. O’Brien points out that there tends to be a link between obesity and vitamin D deficiency. 

“Sun exposure actually triggers the release of nitric oxide which slows weight gain and repairs people’s metabolism,” O’Brien says. “There’s actually evidence that suggests 20 minutes of sunlight a day can improve your body mass index.”

Why is it Important?

Vitamin D is one of the many elements we need to keep our bodies happy and healthy. The three main functions of vitamin D are keeping our bones strong, helping the body to absorb calcium and working with parathyroid glands to maintain healthy levels of calcium.

Emily Van Eck is a registered dietitian and intuitive eating counselor in Austin. She explains the many ways that vitamin D works to help the body function properly.

“In your intestines, vitamin D can help increase calcium absorption from your natural diet,” says Van Eck. “Vitamin D also helps move calcium from the bone into the blood in order to maintain the right concentration. And in the kidney, it helps absorb calcium from the blood. So there is a lot that goes into how vitamin D affects the body.”  

Disorders, such as rickets, which causes weak and soft bones in children, can be caused by a lack of vitamin D in the body. Humans need vitamin D so that calcium and phosphorus can be used to build bones. In adults, having soft bones is a condition called osteomalacia. Weak bones can lead to osteoporosis which is the loss of bone density and can eventually lead to fractures.

Van Eck says that there are also many other roles that vitamin D plays in the body that many people may not know about.

“It can help with preventing cancer cell growth, strengthening the immune system, skin health (especially in those with psoriasis), insulin function, keeping muscles working well, regulating blood pressure and preventing heart disease,” Van Eck explains. “It can also help people with autoimmune diseases, because often these people aren’t getting enough vitamin D.”

Aside from the physical benefits of regular vitamin D supplementation, there are also mental benefits. A study was conducted by the National Center for Biotechnology Information (NCBI) assessing the link between vitamin D and mental health. They found that people with a vitamin D deficiency are more likely to experience depression and seasonal affective disorder. Exposing yourself to just 10 minutes of sunlight a day — especially in the winter — can be a great way to combat the winter blues.

O’Brien explains that a lack of natural light and over-exposure to blue light can impair your body’s circadian rhythms and cause sleep deprivation. Lack of adequate sleep is one of the many factors that can boost symptoms of depression and anxiety as well as inhibit fitness gains.

“Believe it or not, you shouldn’t wear sunglasses when you’re outside,” O’Brien says. “You actually want the sunlight to hit your retina, because that’s going to signal to your body the time of day, which will help with sleep. So next time you go out, ditch the sunglasses — just don’t look directly at the sun.”

How Much Should Someone Take?

The amount of vitamin D you should take daily depends on a variety of factors such as age, weight and daily exposure to sunlight. According to the Institute of Medicine (IOM) committee, infants between the ages of 6 to 12 months should have at least 400 IU but no more than 1,500 IU per day. Children one to eight years of age should be between 600 IU and 3,000 IU, while people over the age of nine should be absorbing between 600 and 4,000 IU per day.

It is important to stay within the recommended daily intake as vitamin D toxicity (hypervitaminosis D) can occur. Although rare, this is a potentially serious condition that occurs when you have excessive amounts of vitamin D in your body. Your body naturally regulates vitamin D from food and sunlight, so this toxicity is typically caused by too much supplementation.

One of the main dangers of vitamin D toxicity is a buildup of calcium in your blood (hypercalcemia). 

“Some symptoms to look out for with vitamin D toxicity are calcification of the kidneys, liver, heart, lungs and blood vessels and possibly symptoms of too much phosphorus in the body, like high blood pressure, nausea and kidney dysfunction,” says Van Eck.

If you are exposed to little or no sunlight or you are overweight, talk to your doctor about taking higher doses of vitamin D.

The Takeaway

Although vitamin D is naturally occurring in the body, it is easy to slip into the danger zone. Whether it be too much or too little, having an imbalance of vitamin D can lead to serious physical and mental health issues. The simplest thing you can do to be sure that you are getting an adequate amount of vitamin D is to get out and enjoy the sunshine and supplement in the winter months if needed. Be sure to include foods in your diet with naturally occurring vitamin D, and enjoy these last few weeks of summer outdoors.


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