The Sunshine Vitamin: Vitamin D

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You’ve got questions about vitamin D and how important it is for your health — and I’ve got answers! Let’s take a look at what you need to know about this important vitamin.

What is Vitamin D and What Does It Do for My Body?

Vitamin D is a key nutrient we all need for optimal health that helps the body properly absorb minerals like calcium and phosphorous.

Vitamin D is involved in almost every system of the body. It helps with:

  • Muscle movement.

  • Nervous system function and message transport.

  • Absorbing, carrying, and depositing calcium in the bones and teeth, which reduces the risk of fractures (ie: Osteoporosis).

  • Regulating cell growth.

  • Immune system function.

  • Reducing inflammation.

This means that if a person’s vitamin D levels are low, they can have all kinds of medical problems. According to the Cleveland Clinic, low vitamin D levels can cause muscle pain, muscle weakness, soft/brittle bones, or osteoporosis. If vitamin D levels are low enough for a long amount of time, a person can even develop Rickets — a disease that causes the legs to bow.

How Do I Get Vitamin D?

Vitamin D is unique in that we get it through multiple pathways. It is the only vitamin that we can acquire through sun exposure to our skin.

Sources of Vitamin D:

  • Sun exposure

  • Sunlight, or UV light, that touches the skin helps the body make vitamin D. However, too much sun exposure increases the risk of skin cancer and early aging of the skin.

  • Foods that contain vitamin D naturally

  • A few oily fish such as salmon and halibut, mackerel, and tuna (cooked using dry heat methods).

  • Fresh mushrooms that have been exposed to sunlight.

  • Vitamin D fortified foods

  • Milk, yogurt, some juices and cereals, and eggs (from hens raised on vitamin D fortified feed).

  • Supplements

However, vitamin D can’t do its job alone. It needs the help of certain organs and body chemistry for activation so that it can work. Let’s jump into a little science!

First, the liver must convert vitamin D into vitamin D2 (calcidiol or 25-hydroxyvitamin D).

Then the kidneys change vitamin D2 into the physiologically active form of vitamin D called vitamin D3 (calcitriol or 1,25 dihydroxy vitamin D).

Types of Vitamins

Vitamins are classified into two groups: fat-soluble and water soluble. Vitamin D is a fat-soluble vitamin which means that it dissolves in fat. This is how it is carried in food and into the bloodstream.

Vitamins A, E, and K also travel with vitamin D and are fat-soluble, as well. This is one of the reasons why you need moderate amounts of healthy fat in your food choices. The body stores these vitamins in body fat, so consuming excess amounts can eventually build up and become toxic. As with most things in life, moderation is key.

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How Much Vitamin D Do I Need?

The Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) established a Recommended Dietary Allowance (RDA) for vitamin D. This represents a daily intake that is enough to maintain bone health and normal calcium metabolism in healthy people and are based on minimal sun exposure.

RDA for Vitamin D (RDAs for vitamin D are often listed in International Units (IU) or micrograms (mcg). This is because of the biological activity of 40 IU = 1 mcg.

  • 0-12 months = 10 mcg (400 IU) per day

  • 1-70, pregnancy, breastfeeding = 15 mcg (600 IU) per day

  • >70 = 20 mcg (800 IU) per day

In addition, the FNB established the Tolerable Upper Intake Level (ULs). ULs are not recommendations; they indicate the maximum intake (daily average) that most likely won’t post risk for health problems for almost all healthy individuals based on current research findings. As intake increases above the UL, the potential risk of adverse health effects increases.

Tolerable Upper Intake (ULs)

  • 0-6 months 1000 IU/day

  • 6-12 months 1200 IU/day

  • 1-3 years = 2500 IU/day

  • 4-8 years = 3000 IU/day

  • 9-18 = 4000 IU/day

  • >19 years, pregnancy, breastfeeding = 4000 IU/day

What Are Some Signs and Symptoms of Vitamin D Deficiency?

It can be tricky to identify a vitamin D deficiency because the symptoms are often unnoticeable or vague. Signs to watch for include things like generalized weakness, fatigue, muscle aches, muscle twitching (fasciculations), osteoporosis (loss of bone mass), osteomalacia (softening of the bones), and depression. In children, irritability, lethargy, developmental delay, bone changes, or fractures are important symptoms of vitamin D deficiency.

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How Prevalent Is the Problem?

People can experience either insufficiency or deficiency of vitamin D. An insufficiency means that people are low in vitamin D, but the situation is not yet a crisis. Once someone has a deficiency, the need for vitamin D is much more urgent and their symptoms are generally more severe.

The US National Health and Nutrition Examination Survey conducted from 2001-2010 showcased the lack of vitamin D with adults.

28.9% of adults had vitamin D deficiency.

41.4% of adults had a vitamin D insufficiency.

Currently, there is lack of evidence for the benefits of screening for vitamin D deficiency. However, with close to half of adults in these surveys having low levels of vitamin D, it’s a great idea for all of us to be aware of our vitamin D intake for ourselves and our loved ones.

What causes Vitamin D deficiency?

Vitamin D nutrient deficiencies are usually the result of dietary inadequacy, impaired absorption/use, increased requirement, or increased excretion. Vitamin D-deficient diets are associated with milk allergy, lactose intolerance, ovo-vegetarianism, and veganism.

People Who Are at Increased Risk for Vitamin D Deficiency Include:

  • Those with kidney disease whose kidneys cannot convert vitamin D2 into vitamin D3.

  • Individuals who have limited sun exposure because either they stay inside all the time, cover up with clothing, or always use sunscreen.

  • Individuals who live in the northern half of the US during cold months in the US don’t get enough sunlight exposure.

  • Those who have inadequate food sources.

  • Breastfeed infants without vitamin D supplementation because human breast milk is not a good source.

  • Older adults because their skin and kidneys don’t tend to work as well.

  • Individuals with dark skin because they can’t produce as much vitamin D.

  • Individuals who are overweight or obese because they can’t convert vitamin D to its active form as well. (In my practice area of adult weight management, approximately 75% of my client population have been diagnosed with Vitamin D deficiency.)

  • Those with other medical conditions such as Cystic Fibrosis, Liver disease, Crohn’s disease, fat malabsorption, or a history of bariatric surgery.

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What Are the Best Ways to Get Vitamin D?

There are several things we can do to ensure we are getting adequate levels of vitamin D.

  • Consume a diet rich in foods with vitamin D.

  • Don’t skip using sunscreen or try other ways to get vitamin D from the sun because direct exposure increases skin cancer risk (unless you check with your doctor about a way to do this in safely for your particular medical history in appropriate doses).

  • If you have concerns, talk with your health care provider prior to supplementing with vitamin D due to toxicity risk. Toxicity can lead to confusion, problems with heart rhythm, and kidney stones, or kidney damage.

Vitamins are essential for human health and function. Our bodies need more of some more than others. How wonderful it is that we can get the vitamins we need through a healthy, balanced diet and that supplements are available if needed.


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Farrah Wigand