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Vitamin D 101 with Expert R.D. Jen Fleming

By: Jennifer Fleming, PhD, MS, RD, LDN

There’s been a lot of buzz around Vitamin D lately, and not just for its benefits on bone health. Studies have shown there’s a strong connection between Vitamin D and immune health, mood health, and much more. But before we dive into the benefits, let’s start with the basics. What is Vitamin D, where can you find it, and how does it work in the body? We asked Registered Dietician & Professor at Penn State, Jen Fleming, PhD, MS, RD, LDN to dive into this powerhouse Vitamin.

Q: Tell me a little bit about Vitamin D.  

A: For starters, Vitamin D is much more than a vitamin. It actually functions more like a hormone. Essentially, your body converts Vitamin D into a steroid hormone that can affect the expression of almost 1,000 different genes in the body. That’s about 4.6% of the human protein-encoding genome, which means it controls over a thousand different physiological processes inside of your body. Let that sink in for a moment!

Q: I’ve heard that sunlight is the best way to get Vitamin D…is that true?

A: Vitamin D is commonly referred to as the “sunshine vitamin” because our bodies produce it after sun exposure. That is, our skin can make Vitamin D upon exposure to UVB radiation. But given the concerns about excessive sun exposure, the best and safest way to increase your Vitamin D levels is by increasing your dietary intake.

Q: So, what foods should I include in my diet if I want Vitamin D?

A: Fatty fish is a good place to start. Salmon, tuna, and mackerel, are among the best sources. Small amounts of Vitamin D are also found in egg yolks, and fortified foods. Fortified foods provide most of the Vitamin D in the American diet. For example, almost all of the U.S. milk supply is fortified with 100 International units (IU) of Vitamin D per cup. But most other dairy products made from milk, such as cheese and ice cream, are not fortified. Ready-to-eat breakfast cereals often contain added Vitamin D, as do some brands of orange juice, yogurt, and margarine and some milk alternatives. But if the goal is to get adequate amounts of Vitamin D for the functional benefits, diet doesn’t account for much at all. That 100 IUs per cup of milk is a drop in the bucket.

Q: Given that we aren’t getting enough Vitamin D through diet and may not even be getting enough via the sun, how do I know I have adequate levels of Vitamin D?

A: Approximately 70% of people living in the US are still Vitamin D inadequate and ~30% are deficient (levels below 20 ng/ml). Unfortunately, most people are not even aware they are lacking Vitamin D.

Since it’s often difficult to assess how much Vitamin D you are getting, it’s a good idea to routinely get your Vitamin D levels tested. Your values will fall into one of three categories:

  • “deficient” (vitamin D levels below 20 ng/ml)
  • “inadequate” (levels between 20 and 29 ng/ml)
  • “adequate” (levels above 30 ng/ml)

The Endocrine Society defines Vitamin D deficiency as below 20 ng/ml (50 nmol/L) because this is the cut-off point where parathyroid hormone levels, which are involved in calcium homeostasis, start to rise outside of healthy ranges. In other words, the physiological definition of Vitamin D deficiency is when the balance of parathyroid hormone begins to shift.

Q: Are there ways I’m compromising my body’s ability to produce Vitamin D?

A: Often unintentionally and related to factors outside of your control. I’ll give you a few examples.

  • Sunscreen use: This is a catch 22. You absolutely want to wear sunscreen to protect your skin. But when it comes to Vitamin D absorption, studies show the use of properly applied sunscreen can reduce Vitamin D absorption by over 95%. To ensure sufficient vitamin D synthesis the typical recommendation is approximately 5 to 30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen. So, if you’re concerned about your skin health, as you should be, this recommendation isn’t going to be feasible.
  • Skin pigmentation: Darker-skinned individuals have more melanin, Melanin acts as a natural sunscreen and, as a result, darker-skinned individuals tend to require more sun exposure than fair-skinned individuals do to generate the same amount of Vitamin D. So, if you have darker skin, you would need to increase the sun exposure time to 20 to 40 minutes per session. Again, this isn’t the best or healthiest solution for your skin.
  • Age: Our body becomes less efficient at producing Vitamin D such that a 70-year old produces four times less Vitamin D than a twenty-year-old! Compared with younger people, older people have lower levels of the substance in the skin that UVB light converts into the Vitamin D precursor. To complicate matters, older individuals tend to spend more time indoors and may not get enough exposure to sunlight.
  • Obesity: From an evolutionary perspective, Vitamin D as a fat-soluble vitamin, accumulates in excess fat tissue as a back-up source when intake is low or production is reduced, such as during the winter months. But studies have also shown that obesity is correlated with low Vitamin D levels. It is theorized that the more fat you have, the more Vitamin D gets stored in that fat, preventing it from making its way to other tissues when needed. It seems counterintuitive but the scientific evidence is sound.
  • Diet: Relying on diet alone is not recommended. Even a great diet that provides adequate amounts of all the vitamins may still lack sufficient Vitamin D. Why? Because very few foods in nature contain Vitamin D. Even the best sources require you load up in order to get the functional benefits. For example, you would need to eat about 5 ounces of salmon, 7 ounces of halibut, 30 ounces of cod, or nearly two 8-ounce cans of tuna to get just 400 international units (IU). An egg yolk will provide about 20 IU, but since it also contains hefty amounts of cholesterol, we don’t recommend the use of eggs to meet your daily needs.
  • Geographic Location: Where you live may be another factor interfering with your Vitamin D production. The further away from the equator you live (latitudes above 37 degrees north or below 37 degrees south of the equator) the less Vitamin D–producing UVB light reaches the earth’s surface during the winter. Residents of Boston, for example, make little if any of the vitamin from November through February!

Q: Knowing all the ways I can become deficient, are there any telltale signs of Vitamin D deficiency?

A: Unfortunately, recognizing a Vitamin D deficiency is not always obvious, but some symptoms, include:

  • Feelings of fatigue or depression. One study reported a prevalence of low Vitamin D among 77.2% in patients who presented with fatigue. Yet, once they increased their Vitamin D levels, fatigue symptom scores improved significantly.
  • Over the long-term, Vitamin D deficiency in adults can potentially lead softening of the bones.
  • More commonly, individuals may reductions in bone mineral density and a loss of muscle mass and strength.

Q: Now that we understand Vitamin D, how we can get it and how we can become deficient, what are some of the benefits of taking a Vitamin D supplement?

A: There’s no doubt Vitamin D is important for many different aspects of your health. But given all the recent news on its connection to immune health, I’ll start there. When the warmth of a nice fire replaces a stroll in the sunny outdoors, it can be more difficult to get Vitamin D. And studies have shown that Vitamin D levels are lowest in the winter months and that the active form of Vitamin D mitigates the damaging inflammatory response of some white blood cells, while it also boosting immune cells’ production of beneficial proteins.

Seasonal depression: Researchers believe that a person’s Vitamin D level may indeed play a role in the risk of seasonal affective disorder (SAD), or seasonal depression, according to the National Institute of Mental Health. People with seasonal affective disorder appear to produce less Vitamin D, which may affect the activity of the neurotransmitter serotonin. Serotonin is known as the feel-good hormone – you know that feeling you get after eating a piece of chocolate! Therefore, when your serotonin level is out of whack, you may feel sad or be at a greater risk for mood disorders.

Heart health: Vitamin D receptors are found within the artery walls as well as the heart. Therefore, it is not surprising to think there may be a link between Vitamin D and heart health.

Q: Thank you for your time, Jen. Any last piece of advice for anyone concerned about their Vitamin D intake?

A: The benefits of Vitamin D are far and wide, and you should take steps to get your recommended daily amount. Ensuring you get enough through food and sunlight is a great first step. But considering supplementation will help you round out your effort to maintain adequate levels of Vitamin D throughout the year. If you suspect that you have a Vitamin D deficiency, talk to your doctor about getting a blood test to check if your level is adequate.

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