Vitamin D: The Sunshine Nutrient That Impacts More Than You Think
- Dr. Gio Feliciano
- Jul 18
- 5 min read
Hello everyone,
We’re in the middle of summer right now, and you might be wondering, “Where have Gio and Chelsea been?” Well, we’ve been taking a little time to rest, get outside, and enjoy the sunshine. It’s actually a perfect way to introduce today’s topic: vitamin D.
You may already know that vitamin D is something we get from the sun. But what does it actually do for your body? And why do so many people feel tired, moody, or off-balance when they’re low in it?
Let’s check it out!
What is vitamin D?
Vitamin D is a fat-soluble vitamin, which means your body stores it in fat tissue instead of flushing it out like water-soluble vitamins. It plays a crucial role in:
Absorbing calcium through your digestive system
Helping your kidneys reabsorb calcium so it’s not lost through urine
Maintaining strong bones and preventing conditions like rickets (in kids) or osteomalacia and osteoporosis (in adults)
But the benefits go way beyond bones. Low vitamin D is also connected to:
Mood changes and brain health
Insulin resistance and type 2 diabetes (Szymczak-Pajor et al., 2020)
Chronic inflammation and autoimmune conditions
What Happens When You're Low?
Low vitamin D can happen to anyone, including me! I was living in sunny California, running outside, enjoying the weather, and still tested low for vitamin D. During that time, I noticed my mood shifting. I was more sensitive to sounds, and my wife could tell something felt wrong. When I saw the results, it made sense.
So how could I be low in vitamin D while getting so much sunshine?
Here’s what I’ve learned:
Body composition matters. If you have very little subcutaneous or an excess of fat tissue, vitamin D may not be stored or released efficiently.
Environmental pollution can block UVB rays, which are needed to produce vitamin D. This makes air pollution one of the main causes of vitamin D deficiency (Barrea et al., 2017). This was probably a major factor for me, since I was living near the city of Los Angeles at the time.
Sunscreen is important for skin protection, but it also blocks the UVB rays your body needs to make vitamin D.
Indoor lifestyles play a big role. Most of us spend our days inside, and when we do go out, it's often early or late when the sun is weaker.
The symptoms of deficiency can be subtle:
Low energy
Mood changes
Fatigue
Poor recovery after workouts
Bone pain (in more severe cases)
Over time, severe deficiency can lead to weak bones that fracture more easily, especially in older adults. In children, it can cause visible bow legs.
How to Get Enough Vitamin D
The best source is sunshine. Your skin produces vitamin D when it’s exposed to UVB rays, especially between 10 a.m. and 4 p.m. However, this is a tricky balance since UVB can also cause sunburn and even skin cancer if you are out for too long. The good news is that you don’t need to spend hours outside to produce vitamin D. Just regular, moderate exposure without getting sunburned is enough to build your stores over time. Recent studies found that you can get the recommended amount of vitamin D by exposing your lower arms and legs to the sun during your regular lunchtime (Webb & Engelsen, 2020).
If you use sunscreen (and I do recommend it), try to get a little sun first. About 10 to 15 minutes can be enough before applying sunscreen to protect yourself.
Other sources include food, though there aren’t many:
Fortified milk and plant milks
Fatty fish like salmon
Egg yolks, especially from pasture-raised chickens
Mushrooms exposed to UV light
Still, for many people, food and sunlight aren’t enough. If you're already low, supplementation might be necessary.
Supplementing with vitamin D
In my clinical experience as a doctor, I've encountered many patients who are low and borderline in vitamin D. In fact, in has become one of the first things I test when evaluating a patient! If you’re not sure about your levels, talk to your doctor. A simple blood test (25-hydroxy vitamin D) can check where you’re at.
What should you look out for?
Most tests will show 30–100 ng/mL as the normal range, although there is a bit of variation here.
Optimal levels are generally considered around 50 ng/mL, since in my experience once you are below that, it becomes very easy to become deficient if you get ill and use up your stores.
For moderate deficiency, a supplement in the 2000–5000 IU range can help patients reach the optimal levels. Tracking vitamin D levels by retesting will help to keep the optimal levels. Doses can be adjusted as necessary or paused and given less frequently.
For severe deficiency, doctors usually prescribe a high-dose supplement like 50,000 IU weekly for a short period. Then we retest and adjust to a maintenance dose.
For maintenance, most adults do well with 600 to 800 IU daily, though needs vary depending on age, weight, skin tone, and lifestyle.
Final Thoughts
You might not feel the effects of vitamin D overnight. But if you’re often tired, low in mood, or dealing with chronic inflammation, it’s worth checking. This isn’t about chasing perfection. It’s about giving your body what it needs to work well and feel well.
So now, let’s think for a moment:
☀️ Are you getting regular sun exposure?
🥣 Are you eating foods that support your vitamin D levels?
📋 Have you ever checked your levels with a provider?
Your body is wise. Let’s support it with what it needs to thrive.
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Feeling low on energy or unsure where to start? Let’s talk about it. Book your discovery call here!
 | Giomarell Feliciano, M.D., MPH, NBC-HWC, is a medical doctor and board-certified health coach who helps busy professionals reclaim their wellness through plant-based nutrition, emotional resilience, and sustainable lifestyle changes. |
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