Vitamin D and Perimenopause: Why You Probably Need More Than You Think

The Vitamin D Gap Most Women Do Not Know About

If your doctor has ever checked your vitamin D level, there is a good chance the result came back low or borderline. You are not alone. Research consistently shows that a significant portion of midlife women are deficient in vitamin D, and most have no idea.

This matters more during perimenopause than at almost any other time in your life. Your hormonal landscape is shifting in ways that directly affect how your body uses and stores vitamin D. Estrogen plays a role in activating vitamin D in the body, so as estrogen levels fluctuate and decline, your effective vitamin D status can drop even if your diet and sun exposure have not changed at all.

The gap between where your vitamin D actually is and where it needs to be can show up as fatigue, low mood, aching joints, increased colds and infections, and even worsened hot flashes. Most of these symptoms are easy to attribute to perimenopause itself, which is why the vitamin D connection often goes unnoticed.

This article breaks down what vitamin D actually does during this transition, how to find out where you stand, and what to do about it if your levels are low.

What Vitamin D Does in Your Body

Vitamin D is technically a hormone, not a vitamin. Your body produces it in the skin when exposed to UVB rays from sunlight, and it travels to your liver and kidneys to be converted into its active form. Once active, it connects with receptors found in almost every tissue in your body.

This widespread receptor presence is why vitamin D affects so many systems at once. It regulates calcium absorption in the gut, which is the foundation of bone health. It modulates immune cell activity, which affects how your body responds to infection and inflammation. It influences serotonin production in the brain, connecting it to mood and sleep quality. Emerging evidence also suggests it plays a role in body temperature regulation, linking it to hot flash severity.

During perimenopause, all of these systems are under pressure. Bone turnover accelerates as estrogen drops. Immune function shifts. Mood regulation becomes more fragile. Getting vitamin D right is not a minor tweak. It is foundational support for a body working harder than usual.

Most adults can produce enough vitamin D from about 15 to 30 minutes of midday sun exposure on bare skin. But many factors reduce how much you actually make: living above 35 degrees latitude, darker skin tone, spending most of your day indoors, wearing sunscreen, and simply getting older. By midlife, skin synthesis of vitamin D from sunlight has declined by roughly 50 percent compared to your 20s.

Vitamin D and Bone Density: The Most Critical Connection

Bone loss accelerates sharply in the years around your final period. In the first five to seven years after menopause, women can lose up to 20 percent of their bone density. Perimenopause is when this process begins to pick up speed.

Vitamin D is essential for calcium absorption in the intestine. Without adequate vitamin D, you can consume all the calcium in the world and still not actually absorb enough of it. Studies show that women with low vitamin D have significantly higher rates of fracture and faster rates of bone mineral density loss than women with sufficient levels.

The protective threshold for bone health appears to be a blood level of at least 30 ng/mL (75 nmol/L), though many researchers argue that 40 to 60 ng/mL offers better protection. This is meaningfully higher than the deficiency cutoff of 20 ng/mL used in some labs, which means you could be told your levels are normal and still not have enough vitamin D to protect your bones well.

Calcium gets most of the attention for bone health, but vitamin D is the gatekeeper. Without it, the calcium in your diet and supplements largely passes through unused. This is why the two are almost always discussed together.

Mood, Cognition, and Sleep

Many women notice their mood becomes harder to manage during perimenopause, and vitamin D is one piece of that puzzle. Vitamin D receptors are found throughout the brain, including in regions involved in mood regulation and cognitive function. Low vitamin D is associated with higher rates of depression and anxiety in the general population, and this relationship appears especially meaningful for women in midlife.

Vitamin D influences the conversion of tryptophan to serotonin, a neurotransmitter that affects mood, appetite, and sleep quality. It also affects dopamine pathways. These are not the whole story behind perimenopausal mood shifts, but correcting a deficiency is one of the simpler things you can do to give your brain better conditions to work with.

Sleep disruption is one of the most common and disruptive symptoms of perimenopause. Vitamin D has been linked to sleep quality in several ways, including its effects on melatonin regulation and its role in reducing nighttime inflammation. Women with low vitamin D tend to report poorer sleep, shorter sleep duration, and more daytime fatigue.

If you are already dealing with brain fog, mood swings, or sleep problems, optimizing your vitamin D is a low-risk, high-upside step worth prioritizing.

Vitamin D and Hot Flashes: What the Research Shows

The link between vitamin D and hot flash severity is still being studied, but the early evidence is encouraging. Some research suggests that women with lower vitamin D levels experience more frequent and more intense vasomotor symptoms (the clinical term for hot flashes and night sweats) than women with higher levels.

One proposed mechanism involves vitamin D role in regulating the hypothalamus, the part of the brain that controls body temperature. When the hypothalamus becomes more sensitive to small temperature changes, as it does when estrogen drops, the result is the sudden perceived overheating of a hot flash. Adequate vitamin D may help stabilize hypothalamic signaling, though researchers are still working out the details.

A 2020 study found that vitamin D supplementation reduced hot flash frequency and severity in women who were deficient. The improvement was not dramatic, but it was meaningful, especially when combined with other approaches. If your hot flashes are frequent and your vitamin D is low, correcting the deficiency is a reasonable first step.

Vitamin D alone is unlikely to eliminate hot flashes, but it may reduce their frequency and intensity while providing the other benefits described in this article. That combination of effects makes it worth taking seriously.

Getting Tested and Understanding Your Results

The test you want is called a 25-hydroxyvitamin D test, sometimes written as 25(OH)D. This is the standard blood test for vitamin D status and is different from the 1,25-dihydroxyvitamin D test, which measures the active form and is used for different purposes.

You can ask your doctor to include it in your annual bloodwork, or you can order it yourself through direct-to-consumer lab services. Reference ranges vary by lab, but here is a practical framework: below 20 ng/mL is deficient, 20 to 29 ng/mL is insufficient, 30 to 60 ng/mL is generally considered optimal for most adults, and above 100 ng/mL is where toxicity concerns begin.

Most conventional guidelines aim to get you above 20 ng/mL, which is enough to prevent serious deficiency diseases. But for the benefits relevant to perimenopause, particularly bone protection, mood support, and immune function, most integrative and functional medicine practitioners aim for 40 to 60 ng/mL.

Testing twice a year is reasonable, especially if you are supplementing. Testing in late winter and late summer gives you a picture of both your seasonal low and seasonal high, which helps you figure out how much to supplement during different times of year.

Dosing, D3 vs. D2, and the Cofactors That Matter

The standard recommended dietary allowance for vitamin D in the US is 600 to 800 IU daily, considered adequate to prevent deficiency disease. For women in perimenopause who are trying to optimize levels, this is almost always too low. Most women with confirmed deficiency or insufficiency need somewhere between 2,000 and 5,000 IU daily to bring levels into the optimal range, with some needing more.

Always choose vitamin D3 (cholecalciferol), not D2 (ergocalciferol). D3 is the form your body produces from sunlight and is significantly more effective at raising and maintaining blood levels. Studies show D3 is roughly two to three times more potent than D2 at comparable doses. Many prescription forms of vitamin D are D2, which is one reason some people see little improvement after being prescribed vitamin D by their doctor.

Vitamin D works best with two cofactors that are easy to overlook. The first is vitamin K2, specifically the MK-7 form. Vitamin D increases calcium absorption, and K2 directs that calcium into bones and teeth rather than into soft tissues like arteries. Without adequate K2, higher vitamin D doses theoretically increase the risk of arterial calcium deposits. Most people are also low in K2 since it is found mainly in fermented foods like natto, which few people eat regularly.

The second cofactor is magnesium. Magnesium is required at multiple steps in the conversion of vitamin D to its active form. If your magnesium is low, your body cannot fully activate the vitamin D you are taking. Magnesium deficiency is extremely common in women under chronic stress or those eating a typical Western diet. Taking vitamin D without adequate magnesium is like filling a car with gas when the fuel line is blocked.

For practical purposes, taking D3 with K2 and ensuring adequate magnesium intake gives your vitamin D supplementation the best chance of actually working. Many combination supplements now include all three.

Food Sources and Sun Exposure

Very few foods naturally contain meaningful amounts of vitamin D. Fatty fish like salmon, mackerel, and sardines are the best whole-food sources, with a serving of wild-caught salmon providing roughly 400 to 600 IU. Egg yolks contain smaller amounts, and some mushrooms exposed to UV light contain vitamin D2. Many foods like milk, orange juice, and cereals are fortified, but the amounts are typically 100 to 400 IU per serving, not enough to significantly move your levels.

Sunlight remains the most efficient natural source. But the reality of modern life, including office jobs, sunscreen use, and living in northern climates, makes consistent solar vitamin D production difficult for most women. From October to April at latitudes above about 35 degrees north (roughly the level of Atlanta, Georgia), the angle of the sun is too low for meaningful UVB penetration. During those months, supplementation is essentially necessary if you want to maintain good levels.

The bottom line on food and sun is that they can help maintain adequate levels if you start from a good place, but they are rarely enough to correct a deficiency or build levels in the optimal range. Targeted supplementation based on your actual lab results is the most reliable approach.

Immune Function and Reducing Infection Risk

Vitamin D is one of the most critical regulators of immune function. Almost every immune cell in the body, including T cells, B cells, macrophages, and natural killer cells, has vitamin D receptors. When vitamin D levels are low, immune cells are less able to mount effective responses to pathogens and less able to regulate inflammatory responses appropriately.

Perimenopause can coincide with a period of increased immune vulnerability. The hormonal shifts of this transition affect immune regulation, and many women notice they get sick more often, take longer to recover, or experience more frequent flare-ups of conditions like cold sores, sinus infections, or urinary tract infections. Low vitamin D is one contributing factor that is addressable.

Vitamin D also plays a role in immune self-regulation, helping prevent the immune system from becoming overactive and attacking the body own tissues. Autoimmune conditions are more common in women than men and often emerge or worsen around the hormonal transitions of perimenopause. While vitamin D is not a treatment for autoimmune disease, maintaining adequate levels is part of a sensible preventive approach.

During cold and flu season, and particularly during months when sun exposure is limited, maintaining vitamin D levels through supplementation is one of the simplest immune-supportive steps available.

Putting It All Together

Vitamin D is one of the most straightforward nutritional interventions during perimenopause because the evidence is strong, the testing is accessible, and the supplementation is inexpensive and safe when used appropriately. It is not a magic solution, but it is a meaningful one.

Start with a test. Find out where you actually are before deciding how much to supplement. Aim for a 25(OH)D level in the 40 to 60 ng/mL range. Choose D3 over D2. Pair it with K2 (MK-7 form, 90 to 200 mcg daily) and make sure your magnesium intake is adequate. Retest after three to four months to see where your levels land.

Tracking your symptoms alongside your supplement routine can help you connect the dots over time. PeriPlan symptom tracking makes it easier to notice patterns, like whether your mood, energy, or hot flash frequency shifts as you optimize your levels.

Vitamin D works best as part of a broader approach that includes nutrition, movement, sleep, and stress management. But for many women, it is one of the highest-impact starting points, especially if you have never been tested or have been told your levels are fine without a closer look.

This content is for informational purposes only and does not replace medical advice. Always consult your healthcare provider about your specific situation.