Many people think getting some sun is enough to top off their vitamin D levels, but the truth is, even with some sunshine, many people are still not getting enough. Here's what you actually need to know about vitamin D, who's at risk, and what to do about it.
Quick Answer
Vitamin D deficiency is linked to fatigue, mood changes, and weakened immunity. If you work indoors, live north of North Carolina, have darker skin, or use sunscreen regularly, you're probably low. A simple blood test costs $30-50 and tells you exactly where you stand. If you're deficient, supplementation usually makes a noticeable difference.
Key Takeaways
- About 1 in 4 Americans are at risk of vitamin D inadequacy; deficiency alone is less common but still affects significant portions of the population.
- You can't always get enough from sun exposure alone — it depends on latitude, skin tone, time of year, and how much time you spend outdoors
- Low vitamin D is linked to weakened immunity, poor mood, muscle weakness, and bone health issues
- Sunscreen blocks about 97% of the UVB rays you need for vitamin D synthesis
Who's at Risk Right Now
You might be vitamin D deficient if you:
- Work indoors most of the day
- Live north of North Carolina
- Have darker skin (requires 3-10 times more sun exposure than lighter skin for the same vitamin D production)
- Use sunscreen regularly
- Are over 60 (your skin synthesizes less vitamin D with age)
- Have digestive issues or obesity that affect nutrient absorption
- Take medications that interfere with vitamin D metabolism
- Follow a diet low in fatty fish, eggs, or fortified foods
The Fatigue-Vitamin D Connection
Feeling unusually tired? Low vitamin D might be why. Research shows that correcting a vitamin D inadequacy through supplementation significantly improves fatigue symptoms, especially in people with documented deficiency.
Why? Vitamin D affects neurotransmitters like serotonin and dopamine (your mood and energy chemicals), reduces inflammation, and supports muscle function. Low levels = exhaustion, brain fog, and weakness. Studies of people with vitamin D deficiency who supplemented at maintenance levels (1,000-2,000 IU daily) showed measurable improvements in fatigue within weeks to months.
The Sun Exposure Question
The sun provides a natural source of vitamin D, so it’s not uncommon to think we can get all we need from a little time outdoors. But the real question is: can the sun really provide an adequate amount, and if so, how long do I need to be outside?
The short answer is: maybe not. It depends on several factors — time of day, season, cloud cover, your skin tone, and whether you're wearing sunscreen. Let's break down why each one matters.
Time of Day and Season
Research shows that in summer, you need about 5-10 minutes of midday sun (between 10 a.m. and 2 p.m.) with roughly one-third of your skin exposed to maintain your existing vitamin D levels. The reason time of day matters so much is that the sun's angle changes throughout the day. When the sun is higher in the sky at midday, UVB rays (the ones that help your body produce vitamin D) penetrate the atmosphere more directly. Early morning or late afternoon sun travels through more atmosphere, and much of the UVB gets scattered before it reaches your skin.
But here's where it gets complicated: that 5-10 minute estimate is for summer. In winter, especially if you live at a northern latitude, the sun never gets as high in the sky. The UVB rays have to travel through much more atmosphere, which means fewer of them actually reach you. In northern latitudes during winter, you'd need 45+ minutes of sun exposure — and that assumes the sun is actually visible and you're willing to be outside in the cold with exposed skin.
Cloud Cover and Geography
Weather matters more than you might think. Cloud cover can reduce UVB rays by 50% depending on latitude and season, which means on an overcast day, even if you're outside for an hour, you're getting significantly less vitamin D-producing radiation than on a clear day. If you live in a region with frequent cloud cover — or if you're going through a season with shorter days and lower sun angles — sun exposure alone becomes increasingly unreliable for maintaining vitamin D.
Skin Tone
Your skin's natural pigmentation directly affects how much vitamin D you can produce from sunlight. Dark skin developed to protect populations who lived in sun-rich environments, where intense UV radiation is constant. Melanin is the pigment that provides this natural protection against UV damage. When you're in the sun, your body produces additional melanin (tanning), but people with darker skin have high baseline melanin levels year-round
That’s why people with darker skin may require upwards of 10 times more sun exposure than people with lighter skin to produce the same amount of vitamin D. This isn't a small difference. If someone with light skin needs 15 minutes in the sun, someone with darker skin might need 30-100 minutes to achieve the same vitamin D replenishment. This is why vitamin D deficiency is significantly more common in people with darker skin tones, particularly those living in northern climates or with limited sun exposure.
Sunscreen: The Catch-22
Here's the dilemma: you're supposed to wear sunscreen to prevent skin cancer. And it works — according to the National Institutes of Health, SPF 30 blocks about 97% of UVB rays, and SPF 50 blocks 98%. But those UVB rays are exactly what your body needs to produce vitamin D. So if you're consistently wearing sunscreen (which you should be for skin cancer prevention), you're also significantly reducing your body's ability to make vitamin D from the sun.
This creates a practical problem: relying solely on sun exposure for vitamin D becomes unreliable when you factor in all these variables. For many people — especially those with darker skin, living in northern climates, working indoors, or conscientiously using sunscreen — the sun alone simply isn't enough. That's where supplementation comes in.
Should I Get Tested for Low Vitamin D?
So, should you get tested? Yes, if you have risk factors above or persistent fatigue, it can be good to rule out if you may be low in vitamin D. A simple blood test (25-hydroxyvitamin D) is usually less than $100 out of pocket and is often covered by insurance, especially if tied into routine annual bloodwork.
Get tested if you have:
- Persistent fatigue that doesn't improve with sleep
- Unexplained muscle weakness or bone pain
- Multiple risk factors (work indoors, northern location, darker skin)
- Mood changes or depression, especially during winter
Knowing your actual vitamin D levels gives you the information you need to make an informed decision about your health. For people with documented vitamin D deficiency or insufficiency, supplementation is often the most practical solution. If your vitamin D levels are low, a daily maintenance dose of 1,000-2,000 IU is typically recommended, and is safe for most people, but your doctor will go over the right dosage for you based on your personal health history and risks. Many people notice significant improvements in energy, mood, and overall well-being once their levels are corrected.
However, supplementation isn't right for everyone, and that's why testing comes first. Talk to your doctor before supplementing if you have a history of kidney stones, sarcoidosis or granulomatous disease, hypercalcemia, or are taking any medications that affect vitamin D metabolism.
The Bottom Line
Vitamin D deficiency is more common than you think and often goes undiagnosed. If you fit any risk categories above, get tested. Understanding your actual vitamin D status is the first step toward addressing deficiency and improving your energy, mood, and overall health.
Ready to check your levels?
Texas Health Physicians Group primary care physicians can order vitamin D testing, discuss supplementation if needed, and help you build a plan for year-round optimal levels.
Find a primary care doctor near you in communities throughout DFW, including Dallas, Fort Worth, Plano, Richardson, Prosper, Flower Mound, and beyond to check your mood changes and immunity.
Sources
- Photochemistry and Photobiology, 2024: Elliott, T.M., et al. "Making the sunshine vitamin — How much sun exposure is needed?"
- National Institutes of Health Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet.
- PMC, 2022: Benefits and Risks of Sun Exposure to Maintain Adequate Vitamin D Levels.