Vitamin D Deficiency in Women: Signs, Risk Factors, and What to Do

Vitamin D deficiency is spectacularly common - by some estimates around a billion people worldwide have low levels - and women carry a disproportionate share of it, because several of the biggest risk factors cluster around female biology and daily life. It is also quiet: most people with low vitamin D feel nothing specific, or feel things vague enough to blame on stress, sleep, or "just life."

Here is what to watch for, who should pay closest attention, and what actually fixes it.

The signs (and why they're easy to miss)

Mild deficiency is usually silent. When symptoms do show up, they tend to be nonspecific:

• Fatigue that does not track with your sleep
• Bone pain or a dull ache - classically in the lower back, hips, or legs
• Muscle weakness, aches, or cramps
• Low mood, sometimes with a seasonal pattern
• Getting sick more often than usual
• Hair shedding in some cases

None of these prove anything on their own - each has a dozen other causes. The pattern to take seriously is several of them together, plus one or more of the risk factors below. Severe, prolonged deficiency is a different story: it softens bone (osteomalacia in adults), causing real bone pain and fractures - rare, but the reason "it's just a vitamin" is the wrong attitude.

Why women specifically

• Pregnancy and breastfeeding. You are mineralizing a second skeleton and then exporting calcium in milk. Requirements stay at 600 IU (15 mcg) daily, and many prenatal vitamins cover this - but deficiency going in is common.
• Menopause. Estrogen loss accelerates bone turnover; adequate vitamin D (plus calcium) is one of the few levers that protect bone density and reduce fracture risk in the decades after.
• PCOS. Low vitamin D is unusually common with PCOS and may worsen the insulin-resistance side of the condition.
• Covered clothing and darker skin. Both dramatically reduce skin synthesis - for cultural dress, that can mean near-zero sun production year-round. Melanin can multiply the sun time needed severalfold.
• Indoor life and sunscreen-first routines. Skincare discipline is great for your skin; it also means many women make very little vitamin D incidentally.
• Higher body weight. Vitamin D is fat-soluble and gets sequestered in adipose tissue, lowering circulating levels.
• Restrictive or low-fish diets. The food list for vitamin D is short: oily fish, egg yolks, fortified dairy or plant milks, some mushrooms. Vegan diets in particular have few natural sources.

The test and the numbers

One blood test settles it: 25-hydroxyvitamin D. The rough bands used by the NIH:

• Below 30 nmol/L (12 ng/mL) - deficient
• 30-50 nmol/L (12-20 ng/mL) - insufficient for some people
• 50 nmol/L (20 ng/mL) and above - adequate for most
• Above 125 nmol/L (50 ng/mL) - too high; linked to adverse effects

If you have symptoms plus risk factors, asking your clinician for this test is entirely reasonable - it is cheap and routine.

Fixing it: sun, food, supplements

• Sun, done sensibly. Skin synthesis is the most efficient natural source - here is how much sun that actually takes for your skin tone and season. Femora's Sunshine feature tracks the vitamin D you make outdoors against the 600 IU daily guideline, so you know whether your sun habit is real or theoretical.
• Food. Oily fish twice a week plus fortified foods helps, but food alone rarely corrects a true deficiency.
• Supplements. The everyday reference points: 600 IU (15 mcg) daily recommended intake for adults, 4,000 IU (100 mcg) safe upper limit unless prescribed more, and the NHS advises everyone consider 400 IU (10 mcg) daily through autumn and winter. Labels switch between IU and mcg constantly - our vitamin D converter translates in one tap. If a test shows genuine deficiency, clinicians often prescribe short courses far above these numbers - that is safe under supervision, not a DIY strategy.
• Recheck. Levels move slowly; retesting after roughly 3 months tells you whether the plan worked.

When to see a doctor

Book in if you have persistent bone pain, muscle weakness, repeated fractures, or the symptom-plus-risk-factor pattern above - and mention vitamin D specifically. If you are pregnant, breastfeeding, or managing PCOS or irregular cycles, vitamin D status is a fair thing to raise at your next appointment anyway.

Low vitamin D is one of the few health problems that is common, quiet, cheap to confirm, and straightforward to fix. That combination is rare - take advantage of it.

Download Femora to track your cycle, symptoms, and daily vitamin D: https://femora.app/download/