Living somewhere sunny does not protect you from vitamin D deficiency. Most people here work indoors, commute in a car, and avoid the heat — and sunscreen, skin tone, body weight, and age all change how much vitamin D you actually make. It usually causes vague symptoms like fatigue and aching, it is diagnosed with a simple blood test, and it is one of the easier problems to correct once you find it.
Key takeaways
Sunshine alone does not prevent deficiency — indoor work and heat avoidance matter more than latitude.
Symptoms are vague and easy to attribute to something else.
Diagnosis is a single blood test; below 20 ng/mL is generally deficient.
Dose should be based on your level, not on whatever is highest on the shelf.
Retest after about three months rather than assuming it worked.
It seems strange to worry about vitamin D in Texas. We have plenty of sun. But I diagnose low vitamin D constantly in Cypress. The sun is only part of the equation.
Why it happens here
Most of my patients work indoors, commute in cars, and spend their weekends inside or in the shade. Add sunscreen, air conditioning, and long work hours, and sun exposure drops fast. In a Houston summer, avoiding the sun is not a lifestyle choice — it is how you get through August.
Several other factors change how much vitamin D your body makes and keeps:
Melanin reduces vitamin D synthesis in the skin, so people with darker skin tones generally need more sun exposure to produce the same amount.
Vitamin D is fat-soluble, so higher body fat can sequester it and lower circulating levels.
Skin synthesis becomes less efficient with age.
Conditions affecting fat absorption — celiac disease, Crohn's, and prior bariatric surgery among them — reduce how much you absorb from food and supplements.
Some medications, including certain seizure medications and steroids, affect vitamin D metabolism.
What low vitamin D feels like
The symptoms are unhelpfully vague, which is a large part of why it goes undetected. Low vitamin D can show up as:
Fatigue
Bone or muscle aches
Getting sick more often
Low mood
Muscle weakness, particularly in the hips and thighs, when deficiency is more significant
Every one of those has other explanations too. Thyroid disease, anemia, sleep problems, and depression all overlap, which is why guessing is a poor strategy and checking the labs is a better one.
Getting tested and treated
The test is a 25-hydroxyvitamin D blood draw, and it does not require fasting. Levels below 20 ng/mL are generally classed as deficient, 20 to 29 as insufficient, and 30 or above as sufficient — though exactly where to draw those lines remains debated among specialists.
Treatment is supplementation, and the right dose depends on how low you actually are. A mild insufficiency and a significant deficiency call for different amounts, and higher-dose regimens are prescribed and monitored rather than picked off a shelf. Vitamin D3 is generally preferred over D2. Because it is fat-soluble, taking it with a meal that contains some fat improves absorption.
Retest after roughly three months. Levels move slowly, and rechecking is the only way to know whether the dose was right. Food sources — fatty fish, egg yolks, fortified milk and cereals — help but rarely correct a real deficiency on their own.
Common questions
How much vitamin D should I take?
It depends on your level, which is why the test comes first. General maintenance dosing for someone in the normal range is very different from correction dosing for someone who is deficient. Bring your bottle to your visit and we will tell you whether what you are taking makes sense.
Can you take too much vitamin D?
Yes. It is fat-soluble, so it accumulates rather than being flushed out. Toxicity is uncommon but real, and it raises calcium levels, which can cause nausea, confusion, kidney stones, and kidney damage. This is the main argument against simply buying the highest-dose bottle available.
How long until I feel better?
Weeks to a few months, and it varies a lot. Some patients notice improvement in energy and aching fairly quickly; others do not notice much at all even as the number corrects. If your level normalizes and you still feel the same, that is useful information — it means we should be looking at something else.
Should I just take a supplement without testing?
A standard over-the-counter dose is unlikely to do harm, but without a baseline you will not know whether it worked or whether vitamin D was the problem in the first place. If you are tired enough to be reading this, the test is worth doing.
The fix is straightforward. Check your level. If it is low, supplement based on your doctor's recommendation, not the highest dose on the shelf. Retest later. This is one of the easiest problems to solve if you actually look for it — and it is part of what we check at an annual physical at FloMD Primary Care in Cypress.
