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Health Information | 05/02/2023

What Is Vitamin D, and Why Is It Important?

By  Dr. Marcy Cheifetz
Growing up, many of us were taught the importance of being outside in the sun to get our “daily dose” of vitamin D. But what exactly is vitamin D, what’s the best way to get it, and why is it important? Vitamin D, or “calciferol,” is both a nutrient we ingest and a hormone our bodies make. Vitamin D helps retain calcium and phosphorus in the body, two vital nutrients in building bone. They are also crucial in helping prevent involuntary contractions of the muscles that lead to cramps and spasms. Studies have suggested that vitamin D may serve other important functions in the body beyond bone health, including:
  • Reducing inflammation
  • Modulating cell growth, neuromuscular and immune function, and glucose metabolism
  • Reducing upper respiratory infections
  • Reducing cancer cell growth
More studies are needed to confirm these other potential benefits of Vitamin D.

Vitamin D Deficiency

Despite many people knowing the importance of vitamin D, it is the most common nutrient deficiency in the world. Roughly 50% of people worldwide experience vitamin D deficiency, and over 30% of adult Americans report low vitamin D levels. In New England, the risk of vitamin D deficiency increases during the colder months, especially in children. A study published by the Journal of Clinical Endocrinology & Metabolism looking at vitamin D in children ages 8-15 in the Greater Boston area found that 90% of them were deficient. There are many reasons someone could be deficient in vitamin D, including:
  • Not getting enough vitamin D in your diet
  • Lack of sunlight exposure
  • Your kidneys or liver can’t activate vitamin D in the body due to a medical condition
  • You take medicine that interferes with your body’s ability to absorb vitamin D
A deficiency in vitamin D may lead to bone density loss and contribute to a higher risk of bone fractures. A severe lack of vitamin D in children can cause rickets, a rare disease that causes the bones to become soft, resulting in muscle weakness, bone pain, deformities in joints, and incorrect growth patterns. In adults, a severe lack of vitamin D can cause osteomalacia, which is associated with bone and joint pain, muscle cramps, bone loss, and an increased risk of fracture.

Getting Enough Vitamin D

The natural way to get vitamin D is by exposing your skin to sunlight. The sun’s ultraviolet B (UVB) rays produce a reaction in your skin cells to produce vitamin D. But getting vitamin D from the sun has its challenges. Even in the warmer months, you need to protect your skin by wearing sunscreen. Sunscreen may reduce the ability of your body to produce vitamin D. Those with darker skin have more melanin, which reduces the amount of light absorbed, so they need to spend more time in the sun to get the same benefit as someone with lighter skin. So how can you ensure you’re getting enough of this important vitamin? The best way to prevent and treat vitamin D deficiency is to increase your vitamin D intake, either through foods or supplements. However, it’s important not to overdo your vitamin D consumption, which can be very harmful. Vitamin D toxicity can lead to nausea, vomiting, constipation, weakness, irregular heartbeat, kidney damage, poor appetite, confusion/disorientation, and weight loss. The key is balance and moderation.

Foods That Contain Vitamin D

Many foods naturally contain some vitamin D and can accommodate various types of dietary restrictions. These include:
  • Fatty fish (salmon, tuna, mackerel, and sardines)
  • Beef liver
  • Mushrooms
  • Egg yolks
  • Cod liver oil
  • Cheese
Some foods are fortified with vitamin D to provide additional nutritional value. When picking fortified foods, check the label to ensure that vitamin D is added.
  • Milk (cow’s milk, soy milk, almond milk, oat milk)
  • Breakfast cereals
  • Orange juice
  • Other dairy products (e.g., yogurt)

Types of Vitamin D Supplements

Supplements are also a convenient and consistent way to boost your vitamin D intake. On the shelves of your grocery store, you might notice that there is vitamin D2 and D3. Both are naturally occurring forms of vitamin D produced by the sun’s ultraviolet-B rays (UVB). The difference between the two is that vitamin D2, or “ergocalciferol,” is produced via plants and fungi, while vitamin D3, or “cholecalciferol,” is produced via animals. Vitamin D3 is generally preferred in supplement form since your body absorbs it better than Vitamin D2, but for those who do not consume animal products, Vitamin D2 is a good alternative. The recommended daily vitamin D intake is between 400-800 international units (IU), varying from person to person based on age and other factors. Some people may require higher doses due to absorption problems or excessive body weight, but most people should not exceed 1000-2000 international units (IU) daily, as too much Vitamin D may actually be harmful. If you are unsure if you’re getting enough vitamin D from your diet and sunlight, connect with your Atrius Health provider about supplement options. Your provider can help determine if you are suffering from vitamin D deficiency and how you can treat it.
Marcy Cheifetz

About The Author

Dr. Marcy Cheifetz

Dr. Marcy Cheifetz joined Atrius Health in 2004 and is an endocrinologist at our Chestnut Hill/West Roxbury practice. She has also served as the director of the Atrius Health Bone Program since 2017, and she manages numerous osteoporosis initiatives for the organization. She received her medical degree from Cornell University Medical College in New York and completed her residency and internship at Yale-New Haven Hospital in New Haven, CT. Dr. Cheifetz’s clinical interests include osteoporosis, diabetes, and thyroid disease. She also routinely performs ultrasounds and biopsies and reads bone densities.

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