Vitamin D: The Sunshine Vitamin

Author: Erica Drost, MS, RDN, LDN
Published: October 17, 2023
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The “Sunshine” Vitamin

The dangers and effects of Covid-19 have been on the forefront of everyone’s mind since Chicago went under lockdown in March.  With the constant threat of infection dominating most people’s health concerns, they are forgetting about the other things that affect their health and happiness, like getting enough sun.  Our time inside has likely increased over the past few months and that can affect many different aspects of our health, including getting sufficient vitamins and minerals. Spending time in the sun is the easiest way to increase Vitamin D in the body, and who doesn’t want another excuse to get outside?

What is Vitamin D?

Vitamin D is the collective name for 2 different vitamins that do very similar things.  Ergocalciferol is vitamin D2 and it is usually found in plants.  Cholecalciferol is vitamin D3 and usually comes from animal products.  Vitamin D is a fat-soluble vitamin whose main function is maintaining calcium levels in the body. Vitamin D acts on the kidneys, bone, and intestines to manage calcium levels in the bloodstream. Maintaining adequate vitamin D in the body leads to more calcium being absorbed from the food we eat, which is why calcium and vitamin D are often paired together in supplements. 

Vitamin D from the diet

The  best sources of vitamin D in our diet come primarily from animal products. The form of vitamin D found in animal products is in the D3 form, which is better utilized by our body. However in plants, generally just have the  D2 form. How the body uses vitamin D2 is not well known, but is believed to have a less potent effect than vitamin D3. Some non-animal products contain vitamin D3, like mushrooms.

There are very few foods that contain vitamin D naturally. The best food sources of vitamin D include fish, (tuna, salmon, mackerel) egg yolks, and beef liver. However there are many foods that are fortified with vitamin D such as milk, orange juice, cheese, and cereals. Foods are fortified with the D3 form of vitamin D. The newest FDA revised Nutrition Fact Labels now require vitamin D content to be listed because many Americans do not get the recommended amount. Check your food labels to make sure you are getting the correct daily recommended intake (DRI). 

Vitamin D from the sun

The first thing that comes to mind when you think about vitamin D is the sun. It’s pretty amazing that our body can use sunlight to make this essential nutrient. The sebaceous glands are responsible for secreting oils that help keep our skin moisturized.  When exposed to sunlight a chemical in these glands called 7-dehydrocholesterol changes.  Over the course of 2 or 3 days the chemical will change into vitamin D3.  It is then released into the body to help manage your calcium levels.

An important thing to note is that sunscreen prevents our skin from making vitamin D. It is actually the ultraviolet light from the sun that sparks the conversion of 7-dehydrocholesterol to vitamin D3. However, that is not an excuse to leave the sunscreen at home! We only need about 38 micrograms(mcg) of Vitamin D every day, and studies have shown that 25 mcg of vitamin D is obtained with only 5-15 minutes of sun exposure. 

The amount of vitamin D created from the sun depends on the time of year, skin color, and age. During the summer months we usually only average about 0.15 mcg of vitamin D created every hour compared to only 0.04 mcg/hour in the winter. People with darker skin often require more sun exposure to make vitamin D than people with fairer skin. Lastly, older people (>50 years) have lower rates of vitamin D creation than younger people.  This means that being outside on a sunny day for a short amount of time will generally provide you with a sufficient amount of vitamin D. Do not worry about sunscreen preventing you from making vitamin D, it only slows down how fast you make it, and if you are going to be out in the sun for any length of time it is worth it to protect your skin from damage.

What happens if I don’t get enough vitamin D?

Some people live in cold climates and do not get much sun exposure throughout the year. Even those who are outside during the summer months may become vitamin D deficient in the winter when sun exposure is less. Under the current circumstances it is not as easy to go outside as much as we would like. As shelter-in-place orders continue, many of us are staying inside consequently affecting not only our activity level, but also our vitamin D levels. 

It is important to be aware of symptoms of vitamin D deficiency. They include bone pain, fatigue, muscle aches, and depression. In children severe vitamin D deficiency can lead to rickets. Visible effects of rickets include bowing of the legs and other bone deformities. In adults the deficiency disease related to vitamin D is osteomalacia, which is the softening of bones. Prolonged osteomalacia can lead to osteoporosis and a greater risk for bone fractures.


Follow these guidelines for preventing and treating osteoporosis:


Preventing osteoporosis: Recommended Dietary Allowance for (RDA) calcium (1,000mg/day for premenopausal women/men) or (1,200mg/day for postmenapausal women) + RDA Vitamin D (15mcg/day)

Treating osteoporosis: RDA calcium (1,000mg/day for premenopausal women/men) or (1,200mg/day for postmenapausal women) + Vitamin D (20mcg/day)


Despite shelter-in-place orders, going outside while maintaining social distancing is still encouraged! Going for a walk, sitting on your porch, or even standing by an open window are great ways to get a little more sunshine. But, if you sit in the sunbeam through a closed window you do not get any of the benefits because glass blocks the type of UV rays that cause your skin to make vitamin D.

Can I have too much Vitamin D?

Vitamin D is one of the most toxic vitamins. In extreme cases excessive amounts of vitamin D can lead to hypercalcemia, or very high levels of calcium in the blood which results in calcification of soft tissues. Organs such as the heart, lungs, and kidneys can become hardened by increased calcium deposition which is extremely dangerous. Vitamin D toxicity can only occur from excessive vitamin D intake in the supplement form. Excessive sun exposure CANNOT cause vitamin D toxicity. It is important to follow the RDA for vitamin D and not go over the tolerable upper limit (TUL).

RDA: 15mcg/day

TUL: 100mcg/day

Should I supplement with vitamin D?

It is important to mention that vitamin D from the sun is the same form as vitamin D from animal sources, D3 form. Most supplement forms of vitamin D are also in the D3 form. Vitamin D2 is not generally used in supplements because it is not as potent. Many calcium supplements and other multivitamins also provide vitamin D. Vitamin D supplementation may be necessary depending on age, diet, underlying health conditions, or the climate in which you live. Vitamin D supplementation may be effective in treating hypertension, preventing type 1 diabetes, and could possibly play a role in obesity prevention. You should always consult a doctor or dietitian before starting vitamin D supplements because of the toxicity effects mentioned above. 

Vitamin D is a vital nutrient needed for the health and maintenance of bones. We should aim to eat food rich in vitamin D, (fish, eggs, and liver) and foods that are fortified with vitamin D (dairy, cereals, and orange juice). Even small amounts of sunlight can be sufficient to meet daily requirements. Supplementation may be necessary for those who live in colder/darker climates. If you think you may need vitamin D supplementation or have questions about your personal health needs make an appointment with a Health Loft dietitian today. 

Submitted by Erica Drost
Edited by Alex Franz
Reviewed by Morgan Murdock



Varady, Kristina. “Vitamin D.”  Nutrition Science II, 3 March 2020, University of Illinois at Chicago, Applied Health Science Building, Chicago, IL. Lecture.

Klemm, Sarah. “What Is Vitamin D.” EatRight, 18 Jan. 2019,

Center for Food Safety and Applied Nutrition, FDA. “Changes to the Nutrition Facts Label.” U.S. Food and Drug Administration, FDA, 2018,

Photo Credit:

 Canva – Woman in Yellow Long sleeve Standing Under the Sunlight

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