Grazing on Vitamin D: Can Sunlight Provide Your Daily Requirements?

It Depends—Supplementation May Be Necessary

By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital
Edited by Kate Findley and proofread by Angela Shoemaker, Wondrium Daily

Vitamin D is one of the rare vitamins that we do not need to get through diet alone—we can make it! Depending on where you live, though, you may want to consider other sources.

Orange juice
Photo By HUIZENG / Shutterstock

Vitamin D Requirements

Despite our ability to synthesize vitamin D through our skin, the Food and Nutrition Board has set daily requirements. The recommended amount is set nationally, disregarding the fact that we get varying levels of sunlight throughout the year.

“I live in Texas, and if you live in Maine, the amount of vitamin D that I can make living in Texas, closer to the equator, is greater than you can,” Professor Anding said.

Five micrograms—not milligrams—or 200 International Units per day is the current requirement for those under 50. In individuals from around ages 51 to 70, synthesis decreases in the skin. The skin becomes less effective at producing vitamin D, and thus the requirement is raised to 10 micrograms for those ages 51 to 70, and 15 micrograms for those over age 70. 

One International Unit is equivalent to 40 micrograms. The effectiveness of these daily requirements is largely dependent on the synthesis of vitamin D in your skin, and many factors can influence that. 

Factors Affecting Exposure

In addition to where you live, skin color is another factor. If you’re African American, you have melanin in your skin that acts as a natural sunscreen, and you don’t make as much vitamin D. Additionally, if you wear sunscreen, you can reduce the synthesis of vitamin D in your skin.

Generally it takes 10 to 15 minutes for sunscreen to be activated, so if you put sunscreen on right as you walk out the door, you’re still going to have some synthesis of vitamin D in your skin. Generally, 10 to 15 minutes per day at the peak sun level is a good amount of exposure. 

“We’re not promoting sunburn; we’re not promoting skin cancer,” Professor Anding said. 

You should also factor in the time of year and your clothing when considering whether or not you’re getting adequate vitamin D exposure through the sun. If you live in Chicago, you’re probably not exposing your arms and legs in January. Realistically, then, your clothing could be a barrier based on the season of the year.

Vitamin D Sources

Only a few food sources contain vitamin D, and they are almost all fortified. Milk can be fortified, and if you get skim milk where they’ve skimmed off all the fat, the label will indicate that it’s fortified with vitamins A and D—both fat-soluble vitamins lost in the cream. Breakfast cereals are often fortified with vitamin D, as well as orange juice, where the blue label indicates that calcium and vitamin D have been added. 

Natural sources of vitamin D include egg yolk and butter. Oily fish, which includes salmon or cod liver oil, can also a good source of vitamin D.

“The cod liver oil your grandma gave you was purer than the cod liver oil that you can buy now, and so oily fish would be a better option for you,” Professor Anding said.

When it comes to disorders related to vitamin D, the classic vitamin D deficiency disorders are rickets and osteomalacia. Osteomalacia refers to a softening of the bones and is a little different than osteoporosis, which means the bones become brittle. 

Although this is relatively rare, taking any kind of anti-seizure medication—for epilepsy, for example—can actually enhance the destruction of vitamin D. Left untreated, it can increase the development of bone disease. 

“I’ve actually seen rickets in Houston in a girl who was a blue-eyed blonde,” Professor Anding said. “Why would a blue-eyed blond with fair skin end up with rickets? Because of sunscreen. She never left the house without sunscreen, and she refused, absolutely positively refused, to drink milk.”

Keep in mind that many people today drink vegan products such as soy milk, rice milk, and almond milk. You need to read the label to see whether or not vitamin D is included in that product because it’s not there naturally.

This article was edited by Kate Findley, Writer for Wondrium Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for Wondrium Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.