The only definitive way to know if you have a vitamin D deficiency is through a blood test, but several physical symptoms and risk factors can signal that your levels are low. Vitamin D deficiency is common, and its symptoms overlap with many other conditions, which means it often goes undiagnosed or gets mistaken for something else entirely.
Symptoms That Point to Low Vitamin D
Vitamin D deficiency doesn’t always announce itself with obvious signs. Many people with low levels feel fine, at least initially. When symptoms do appear, they tend to be vague enough that both patients and doctors can chalk them up to other causes.
The most characteristic symptoms are bone pain, muscle aches, and a generalized weakness that doesn’t improve with rest. These musculoskeletal complaints are so frequently tied to low vitamin D that researchers have suggested routine testing for anyone who presents with them, since they’re commonly misdiagnosed as fibromyalgia, chronic fatigue syndrome, age-related weakness, or depression. Fatigue is especially tricky because it has dozens of possible explanations, but persistent, unexplained tiredness combined with muscle soreness or bone tenderness should raise the question of vitamin D status.
Less obvious signs include hair thinning and increased shedding. Research shows an inverse relationship between vitamin D levels and several types of non-scarring hair loss. Slow wound healing and frequent infections have also been linked to deficiency, since vitamin D plays a role in immune function. Mood changes, particularly feelings of depression, show up in some people with low levels, though the connection is complex and not fully one-directional.
Who Is Most at Risk
Your body manufactures vitamin D when ultraviolet B rays from sunlight hit your skin. Anything that reduces that exposure increases your risk of deficiency.
Skin pigmentation is one of the biggest factors. Melanin, the pigment that gives skin its color, absorbs UVB radiation before it can trigger vitamin D production. African Americans have a 15- to 20-fold higher prevalence of severe vitamin D deficiency compared to European Americans. The same principle applies to immigrants from Mexico, South Asia, and other regions with darker average skin tones who now live at higher latitudes.
Geography matters independently of skin color. UVB radiation decreases as you move farther from the equator, so people living in the northern United States, Canada, the UK, and northern Europe produce less vitamin D from sunlight year-round. The combination of darker skin and a northern location compounds the problem significantly. Older adults also produce vitamin D less efficiently in the skin and tend to spend more time indoors. People who are homebound, work night shifts, wear clothing that covers most of the body, or live in heavily polluted cities face similar challenges.
How Sunlight and Sunscreen Factor In
You don’t need hours of sun to make vitamin D, but you do need direct, unfiltered UVB exposure. The general guideline is to get about half the amount of sun it would take to cause a very mild sunburn (slight pinkness 24 hours later), then cover up or apply sunscreen. Exposing roughly 20% of your body, think forearms and lower legs, to that amount of UVB is equivalent to ingesting about 1,400 to 2,000 IU of vitamin D.
Sunscreen with SPF 30 absorbs 95 to 98% of UVB radiation, reducing your skin’s ability to produce vitamin D by the same percentage. That doesn’t mean you should skip sunscreen, but it does explain why people who are diligent about sun protection can still end up deficient. Glass blocks all UVB radiation as well, so sitting by a sunny window does nothing for your vitamin D levels.
The Blood Test That Confirms It
A 25-hydroxy vitamin D blood test is the most accurate way to measure your vitamin D status. It’s a standard blood draw, usually doesn’t require fasting, and results come back with a number measured in nanograms per milliliter (ng/mL).
Here’s how to read your results, based on ranges established by the National Academies of Sciences, Engineering, and Medicine:
- Below 12 ng/mL: Deficient. This level is associated with bone-softening diseases in adults and rickets in children.
- 12 to 19 ng/mL: Inadequate for bone and overall health.
- 20 ng/mL or above: Generally sufficient for most people.
- Above 50 ng/mL: Potentially too high, with risk of adverse effects climbing above 60 ng/mL.
There is no blanket recommendation to screen everyone. The U.S. Preventive Services Task Force currently says there isn’t enough evidence to recommend routine screening for adults who have no symptoms and no conditions that would warrant treatment. In practice, this means you’ll typically need to ask your doctor for the test or have a reason, such as symptoms or risk factors, for them to order it.
At-Home Tests vs. Lab Draws
At-home finger-prick vitamin D tests are widely available and can give you a reasonable estimate. Research comparing point-of-care tests to standard lab methods found a strong correlation (r = 0.89), meaning they track closely with conventional results for most people. Their reliable range is between 10 and 100 ng/mL.
The catch: if your result comes back below 30 ng/mL, researchers recommend confirming with a standard lab test before making supplementation decisions. The same applies for readings above 80 ng/mL, where accuracy drops. Home tests are a useful screening tool, but they’re not precise enough at the extremes to guide treatment on their own.
What Happens if Deficiency Goes Untreated
Short-term, low vitamin D produces the aches and fatigue described above. Over months and years, chronic deficiency leads to more serious skeletal problems. In adults, the primary concern is osteomalacia, a condition where bones soften because they can’t mineralize properly. This causes deep bone pain and makes bones vulnerable to fractures from minimal or no trauma. These fractures commonly occur in the hip, pelvis, and spine. In children, the equivalent condition is rickets, which affects the growth plates and can cause lasting skeletal deformities.
Long-standing osteomalacia can also lead to spinal curvature. The fracture risk from osteomalacia is distinct from osteoporosis, though the two conditions can overlap, with osteoporosis involving loss of bone density and osteomalacia involving poor mineralization of the bone that remains.
Practical Steps if You Suspect Deficiency
If you have multiple risk factors or persistent symptoms like bone pain, muscle weakness, or unexplained fatigue, getting a blood test is the clearest path forward. You can request one from your primary care provider or use a home test as a first step.
For people with darker skin living far from the equator, some researchers suggest supplementing with vitamin D3 to bring levels to at least 30 ng/mL, since dietary sources alone rarely provide enough. Fatty fish, fortified milk, and egg yolks contain some vitamin D, but the amounts are modest compared to what your skin can produce from even brief sun exposure. A few minutes of midday sun on bare skin several times a week, when UVB levels are adequate for your latitude, can make a meaningful difference for lighter-skinned individuals, though this becomes less practical in winter months at northern latitudes.