Vitamin D is often called the "sunshine vitamin," but here's a startling fact: up to 42% of American adults are vitamin D deficient - and women are at even higher risk.
What's more concerning? The standard "normal" range used by most labs may be set far too low. You could have a technically "normal" vitamin D level and still be suffering from deficiency symptoms.
What Does Vitamin D Actually Do?
Vitamin D isn't just about bone health. It functions more like a hormone and influences nearly every system in your body:
- Immune function: Regulates immune response and helps fight infections
- Mood and mental health: Low levels linked to depression and anxiety
- Energy production: Essential for mitochondrial function
- Hormone regulation: Influences estrogen, testosterone, and insulin
- Fertility: Impacts ovulation and implantation
- Thyroid function: Vitamin D deficiency is common in autoimmune thyroid conditions
- Bone health: Necessary for calcium absorption
- Muscle function: Deficiency causes weakness and pain
Symptoms of Vitamin D Deficiency
Deficiency symptoms are often vague and easily dismissed as "just stress":
- Fatigue that doesn't improve with sleep
- Depression or persistent low mood
- Muscle weakness or aches
- Bone pain, especially in the back
- Frequent illness or infections
- Hair loss
- Slow wound healing
- Brain fog or difficulty concentrating
The "Normal" Range Problem
Most labs define vitamin D (25-OH) levels as:
- Deficient: Less than 20 ng/mL
- Insufficient: 20-29 ng/mL
- Normal: 30-100 ng/mL
Here's the issue: many people feel terrible at 30 ng/mL. This level may be enough to prevent severe deficiency diseases like rickets, but it's not optimal for energy, mood, and overall function.
Optimal vitamin D levels are typically 40-60 ng/mL. Some functional medicine practitioners aim for 50-80 ng/mL, especially for autoimmune conditions.
Why Are Women More At Risk?
Several factors put women at higher risk for vitamin D deficiency:
- Body fat: Vitamin D is fat-soluble and can get "trapped" in fat tissue
- Sunscreen use: SPF 30 blocks about 97% of vitamin D-producing UVB rays
- Indoor lifestyles: Office jobs mean less sun exposure
- Darker skin: Higher melanin reduces vitamin D synthesis
- Northern latitudes: Limited UVB exposure, especially in winter
- Pregnancy and breastfeeding: Increased requirements
- Age: Skin produces less vitamin D as we age
Vitamin D and Women's Health Conditions
PCOS
Studies show that 67-85% of women with PCOS have vitamin D deficiency. Low vitamin D is associated with worse insulin resistance, higher androgens, and more severe symptoms. Supplementation may improve metabolic markers.
Autoimmune Conditions
Vitamin D deficiency is extremely common in Hashimoto's thyroiditis, lupus, rheumatoid arthritis, and multiple sclerosis. Adequate levels may help modulate the immune response.
Fertility
Vitamin D receptors are found in the ovaries, uterus, and placenta. Deficiency has been linked to lower IVF success rates and increased risk of pregnancy complications.
Depression and Anxiety
Multiple studies link low vitamin D to increased risk of depression. While not a cure-all, optimizing levels may support mental health.
Getting Tested
The test you need is 25-hydroxyvitamin D (25-OH vitamin D). This measures your body's stored vitamin D and is the standard marker for assessing status.
Things to know:
- Levels can vary seasonally (lower in winter, higher in summer)
- Testing 2-3 months after starting supplementation shows response
- Very high doses require monitoring to avoid toxicity (though rare)
Raising Your Vitamin D Levels
Sun Exposure
10-30 minutes of midday sun on bare skin (arms and legs) a few times per week can help - but this isn't practical for many people, especially in northern climates or winter months.
Food Sources
Very few foods naturally contain vitamin D:
- Fatty fish (salmon, mackerel, sardines)
- Egg yolks
- Fortified foods (milk, orange juice, cereals)
- Mushrooms exposed to UV light
Diet alone rarely provides enough vitamin D for optimal levels.
Supplementation
Most people need supplementation to reach optimal levels. Vitamin D3 (cholecalciferol) is preferred over D2. Dosing depends on your current levels - someone severely deficient may need 5,000-10,000 IU daily initially, while maintenance might be 1,000-2,000 IU.
Important: Vitamin D is fat-soluble, meaning it accumulates in your body. Always test your levels before starting high-dose supplementation, and retest periodically to ensure you're in the optimal range without going too high.
The Bottom Line
If you're dealing with unexplained fatigue, depression, frequent illness, or just feeling "off," vitamin D deficiency could be a contributing factor. Don't accept a level of 30 ng/mL as "fine" if you're still symptomatic - optimal is 40-60 ng/mL for most people.
Testing is simple, and addressing deficiency can have profound effects on how you feel.
Know your levels. Get your Vitamin D tested along with other essential nutrients that power your health.
Sources
- Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. JAMA Intern Med. 2011.
- Thomson RL, et al. Vitamin D in the aetiology and management of polycystic ovary syndrome. Clin Endocrinol. 2012.
- Kim D. The role of vitamin D in thyroid diseases. Int J Mol Sci. 2017.