Vitamin D: Do you know what your levels are?

Author: ​Chantelle van der Merwe

Registered Dietitian (SA) . PG Dip Diabetes Management (UK). All about Real nutrition for Real, every-day life ​

Vitamin D: How Low is Too Low?

Why I check my patients’ vitamin D levels: Even living in sunny South Africa, I’m often surprised by how many clients present with levels below 20 ng/mL. Despite all the sunshine, people simply aren’t getting outdoors enough — and while some foods do contain vitamin D, it’s very difficult to meet your needs through diet alone. Your main source remains the sun.

I often call vitamin D the “happy vitamin” or the “sunshine vitamin.” Think sunshine, think happy: happy mood, happy bones. But when it comes to deciding what counts as a “healthy” vitamin D level, things get a little complicated.
An excellent article by Dr. M. Tello, featured on the Harvard Health website, explores just how much controversy exists around this topic.

The Debate Around “Normal”

• Institute of Medicine (2010): Suggested that a vitamin D level of 20 ng/mL or higher is enough for good bone health, with levels below 20 considered deficient.
• Endocrine Society (2011): Took a stricter stance, recommending a minimum of 30 ng/mL, and ideally between 40–60 ng/mL, for both adults and children.
• New England Journal of Medicine (2015): Some experts pushed back, arguing that deficiency is over diagnosed. They proposed that the true cutoff should be much lower — around 12.5 ng/mL — which would drastically reduce the number of people considered deficient.

As you can see, the goalposts shift depending on which authority you follow.

Why the Confusion?
Vitamin D levels are influenced by diet, sun exposure, skin tone, and even where in the world you live. Some researchers argue that humans evolved to tolerate a wide range of vitamin D status, which makes it difficult to draw a single line in the sand for everyone.

Who Really Needs Testing?
Experts agree that not everyone needs routine vitamin D screening. Instead, testing is most important for people at higher risk, such as:

• Those with osteoporosis or osteopenia
• People with digestive conditions that affect absorption (e.g., celiac disease, gastric bypass surgery)
• Individuals with darker skin or who avoid sun exposure
• Pregnant or breastfeeding women

My Perspective in Practice
In my own work, I find it practical to use 20 ng/mL as a safe minimum threshold. While some experts argue that lower levels may be “good enough,” I have repeatedly seen clients with levels below 20 experience fatigue and low energy. Once they begin supplementation and bring their levels above 20, they often report feeling more energetic and healthier overall.
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So while the debate continues in research circles, my approach is simple: better safe than sorry. Keeping levels above 20 offers peace of mind, supports bone health, and — in my experience — improves overall well-being. So, if you fall in the "higher risk" category, let's get those levels checked!