What is the Connection Between Vitamin D and Sunlight?

B. Schreiber

The body's natural production of vitamin D in the skin, which is accomplished with the help of radiation from the sun, is the primary connection between vitamin D and sunlight. The production of vitamin D is one of the primary functions of the skin, along with more obvious features like feeling and insulation. When the skin is struck by ultraviolet light from the sun, it produces a substance that the body can convert into vitamin D. In areas with strong enough sunlight, regular exposure to the sun's rays can produce enough vitamin D to meet the body's requirements. Due to the connection between vitamin D and sunlight, this vitamin is often informally called the sunshine vitamin.

The body converts ultraviolet-B rays from the sun into vitamin D.
The body converts ultraviolet-B rays from the sun into vitamin D.

The synthesis of vitamin D in the skin begins when a modified type of cholesterol naturally present in skin cells is exposed to sunlight. Specifically, the molecule is exposed to an invisible type of light, known as ultraviolet B (UVB), which converts it into a substance called cholecalciferol. Cholecalciferol is then transmitted through the bloodstream to the liver and kidneys, where it is further modified to become the active form of vitamin D, also known as calcitriol. The relationship between vitamin D and sunlight helps the body carry out a number of important functions. The most important of these is the maintenance of healthy bones and teeth.

Sunlight aids the natural production of vitamin D in human skin.
Sunlight aids the natural production of vitamin D in human skin.

Differing geographical locations can affect the relationship between vitamin D and sunlight. In northern latitudes, weaker and less frequent sunshine reduces the skin's opportunities to manufacture the vitamin D precursor. Also, since such climates tend to be colder, people are more likely to wear heavy clothing and spend more time indoors, further decreasing time spent in the sun.

A lack of sunlight during the winter months may cause seasonal affective disorder (SAD) in some people.
A lack of sunlight during the winter months may cause seasonal affective disorder (SAD) in some people.

Pollution and cloud cover can also reduce the amount of ultraviolet light that reaches the earth's surface. Still, five to 15 minutes of daily, unprotected exposure to sunlight is probably enough to meet most peoples' need for vitamin D. Longer periods of exposure to the sun's rays increases the risk of skin cancer. It also makes the skin age more quickly, which increases the occurrence of wrinkles and spots.

While environmental factors can disrupt the relationship between vitamin D and sunlight, this vitamin can also be obtained through food or supplement sources, where it is absorbed in the intestine. Good food sources of vitamin D include cold-water fish, egg yolks, and fortified foods like milk or breakfast cereals. Vitamin D can also be purchased as a supplement and is usually included in multivitamin formulas.

According to experts, just 5 to 30 minutes of sunlight daily enables the body to generate a sufficient amount of vitamin D.
According to experts, just 5 to 30 minutes of sunlight daily enables the body to generate a sufficient amount of vitamin D.

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Discussion Comments


I am very fair-skinned, so I can only spend about ten minutes without sunscreen when I'm outside. I make it a point to do this, though, because I want to be getting all the vitamin D I need from the sun.

I have an outdoor pool, and I have to apply a waterproof 30 SPF sunscreen before I swim. However, there are plenty of things I have to do before getting into the water, like gathering up the skimmer, floats, and noodles from the shed.

I go without sunscreen while I transport these items to the pool. I carry them one at a time, so I spend more time in the sun and get more exercise.

After ten minutes is up, I go into the shade and spray on the sunscreen. They say that it takes awhile for the sunscreen to soak in and really do its job, so I may be getting more than ten minutes worth of vitamin D!


@lighth0se33 – It's kind of cool that lack of sunshine can cause depression. It's as though our bodies know that they need it, and when we deprive them of it, it makes them sad.

I have always had the instinctual urge to go outside as much as possible. I work at home, and I make sure to take off early enough to spend time in the sun every day.

Rainy days are so depressing to me, and if for some reason I have something to do that takes all day, I go crazy because I can't be outside! I'm sure that I have plenty of vitamin D in my system, because my mind and body won't let me have a shortage!


@seag47 – Hearing about people who live in areas where they can't absorb the sun's rays for months out of the year really makes me appreciate the mild winters where I live. My friend, who used to shut herself inside all the time, has also learned to appreciate our climate since her bout with a vitamin D deficiency.

She was a city girl, and she had no desire to be outdoors. Because of this, her body suffered from the lack of vitamin D. She became very depressed, and she frequently got upper respiratory infections.

Her doctor told her that she needed to get some sun. He said that her depression was likely seasonal affective disorder, which is what people get during the winter when the sun goes down so early and they don't have the chance to get out in it.

After taking her course of antibiotics to treat her existing infection, she began going for walks in the park with me every day that the weather permitted. Her mood improved after the first day of this, and she saw what she had been missing all along.


My husband's family lives in New York, so they suffer through some bitterly cold winters. When the ground is covered in snow, it is just too cold to be going out without most of their bodies covered.

So, they have to settle for vitamin D from food sources during these icy months. They eat fortified milk with their fortified cereal, and they also drink the milk at other times of the day.

He told me that they make it a point to eat tuna once a week, since it is a good source of vitamin D. They also eat eggs several times a week.

As far as he knows, none of them have suffered symptoms of a vitamin D deficiency. The food source trick must be working.

In the summer, they absorb plenty of sun. They appreciate the warmth so much while they can, because they know it won't be around for very long.


@ElizaBennett - I didn't know that about sun and sleep! I'll be taking my baby daughter out for a walk this afternoon to see if it works for kids, too!

I've also heard that vitamin D is stored in the body's fat cells. So if you normally get a lot of sun, you might not need to take a supplement on rainy days. It's not like vitamin C, which apparently you have to take every single day as the body can't store it.

But that also means you have to be careful not to get too much vitamin D. Most people don't get nearly enough, but if you eat a lo of fortified foods, take both a calcium supplement and a multivitamin, and spend a lot of time outside, you could get too much and get really sick.


Getting more sun is the most natural way to treat a lack of vitamin D, and it has other benefits as well - studies show that getting more sun during the day helps people sleep better at night, for instance.

But be sensible. If the weather is warm enough to leave your arms and legs uncovered, let those soak up the vitamin D while you protect more sensitive areas. Put a broad-sunscreen sunscreen on your face, neck, and the backs of your hands, as those are the places most likely to get skin cancer. (Ladies may also want to protect their decolletage if their shirt doesn't cover it - that site is one sure give-away of a lady's age.)

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