Vitamin D and Perimenopause: A Guide to Deficiency, Testing, and Why It Matters

Why vitamin D is particularly important during perimenopause

Vitamin D is often called a vitamin, but it functions more like a hormone. Receptors for vitamin D are found throughout the body, in bone, muscle, brain, immune cells, gut, and reproductive tissue. It regulates hundreds of genes and is involved in calcium absorption, immune function, mood regulation, muscle strength, and inflammation control.

During perimenopause, vitamin D becomes particularly important for several intersecting reasons. Bone loss accelerates as estrogen declines, and vitamin D is essential for calcium absorption and bone mineralization. Muscle loss also accelerates during this transition, and adequate vitamin D supports muscle function and reduces fall risk. Inflammation rises as estrogen regulation weakens, and vitamin D has well-documented anti-inflammatory effects. Mood and cognitive changes are common in perimenopause, and deficiency is associated with depression and cognitive decline.

Despite how much the body depends on it, vitamin D deficiency is remarkably common. Estimates suggest that over 40 percent of adults in the United States have insufficient levels, and the figure is higher in women in midlife, especially those in northern latitudes, those who avoid sun exposure, and those with darker skin, which requires more sunlight to produce the same amount of vitamin D.

Symptoms of vitamin D deficiency and how they overlap with perimenopause

The symptoms of vitamin D deficiency overlap substantially with the symptoms of perimenopause itself, which is one reason deficiency often goes undetected during this transition.

Fatigue is among the most common symptoms of deficiency. It is a heavy, persistent tiredness that does not fully resolve with adequate sleep, distinct from the fatigue driven purely by sleep disruption. In perimenopause, where fatigue is already prevalent, deficiency-related fatigue compounds the problem and may be overlooked.

Bone and muscle pain, particularly diffuse aching that is hard to localize, is a recognized sign of severe deficiency. More moderate deficiency may produce subtler musculoskeletal discomfort that is easily attributed to perimenopause joint changes.

Mood changes, including low mood, depression, and anxiety, are associated with low vitamin D. Several studies have found that vitamin D supplementation reduces depressive symptoms, though effect sizes vary and deficiency is one of many factors involved in mood.

Frequent illness and slow recovery may reflect impaired immune function linked to deficiency, since vitamin D is required for the activation of immune cells.

Cognitive symptoms including memory difficulties and brain fog have been associated with low vitamin D in research, though the direction of causation and the degree of effect are still being studied.

Because these symptoms mirror perimenopause so closely, testing is the only reliable way to know whether deficiency is contributing to your symptom load.

Testing: what to ask for and how to interpret results

The standard test for vitamin D status is a blood test measuring 25-hydroxyvitamin D, often written as 25(OH)D. This measures the storage form of vitamin D in the body, which reflects both dietary intake and sunlight exposure over the preceding weeks to months.

Reference ranges vary slightly by lab, but general consensus among research and clinical organizations defines:

Deficiency as below 20 ng/mL (50 nmol/L). Insufficiency as 20 to 29 ng/mL. Sufficiency as 30 to 100 ng/mL. Optimal for most health outcomes appears to be in the range of 40 to 60 ng/mL based on research, though some organizations use higher targets for specific conditions.

Many standard blood panels do not automatically include vitamin D. You may need to ask for it specifically. If you have never had your level tested, or if it has been several years since your last test, requesting it at your next routine check is straightforward.

It is worth retesting after supplementing to confirm your levels have reached the target range. Some people need higher doses than others to achieve the same blood level, depending on absorption efficiency, body weight, and baseline deficiency.

How much vitamin D to take and what form works best

Vitamin D supplementation recommendations depend on your baseline blood level, your sun exposure, your diet, and your health goals.

The current official dietary reference intake for vitamin D (RDA) for adults is 600 to 800 IU per day, but many researchers and clinicians who work with vitamin D consider this too conservative, particularly for people who are already deficient or insufficient. Doses of 1,000 to 2,000 IU daily are widely used in clinical practice for maintenance in people with adequate levels. For people who are deficient, healthcare providers commonly recommend higher loading doses (such as 3,000 to 5,000 IU daily) for several months before testing to re-establish adequate stores.

Vitamin D3 (cholecalciferol) is the preferred form. It is the same form the skin produces from sunlight and is more effective at raising blood levels than vitamin D2 (ergocalciferol).

Vitamin D is fat-soluble and is absorbed much better when taken with a meal that contains fat. Taking it with breakfast or dinner rather than on an empty stomach significantly improves absorption.

Vitamin D and vitamin K2 work together in calcium metabolism. Vitamin D increases calcium absorption, and vitamin K2 helps direct that calcium to bones rather than soft tissue and arteries. Many vitamin D supplements now include K2 for this reason. If you are taking high-dose vitamin D and do not get dietary K2 (from fermented foods and animal products), a combined supplement may be worth considering. Discuss this with your provider if you take blood-thinning medications, since vitamin K can affect coagulation.

Sunlight, diet, and non-supplement sources

Sunlight exposure is the most natural way to maintain vitamin D levels. When UV-B rays hit the skin, they convert a cholesterol precursor into vitamin D3. The amount produced depends on the time of day, season, latitude, skin tone, age, and how much skin is exposed.

For most people at northern latitudes (above 35 degrees north, which includes most of the northern United States, Canada, and Europe), meaningful vitamin D synthesis from sunlight is limited to the summer months and is essentially zero from October through March. Even during summer, exposure before 10 am or after 3 pm produces little vitamin D because UV-B angles are too low.

Midday sun exposure (10 am to 2 pm) with arms and legs exposed for 15 to 30 minutes (shorter for lighter skin, longer for darker skin) produces meaningful vitamin D. Sunscreen blocks this synthesis, so a window of unprotected midday sun exposure is the traditional recommendation, though this must be balanced with skin cancer risk. Brief exposure rather than extended unprotected time is the practical approach.

Dietary sources of vitamin D are limited but include fatty fish (salmon, sardines, mackerel), egg yolks, and liver. Fortified foods such as milk, plant milks, orange juice, and cereals contribute small amounts. Diet alone is rarely sufficient to maintain optimal blood levels without either regular sunlight or supplementation.

Vitamin D, bone health, and perimenopause

The most direct clinical application of vitamin D in perimenopause is bone health. Calcium cannot be properly absorbed from food or supplements without adequate vitamin D. Even a calcium-rich diet provides limited skeletal benefit if vitamin D is deficient.

The rapid bone loss that characterizes the perimenopausal and early postmenopausal period, which can total 10 to 20 percent of lifetime bone mass, is partially modifiable. Adequate vitamin D and calcium intake, combined with resistance training and impact exercise, represent the nutritional and lifestyle foundation of bone protection.

For women who are at risk of osteoporosis (which includes virtually all women in perimenopause to some degree, with higher risk from family history, low body weight, smoking, heavy alcohol use, or corticosteroid therapy), ensuring optimal vitamin D status is not optional. It is a baseline intervention that should precede any more complex bone health conversation.

Tracking your physical symptoms, including muscle pain, fatigue, and joint function, in PeriPlan over the weeks after beginning vitamin D supplementation can help you notice whether deficiency-related symptoms are improving. Full resolution of symptoms related to deficiency typically takes several months of consistent supplementation at adequate doses.

This article is for informational purposes only. Always consult your healthcare provider for testing, dosing guidance, and management of any deficiency or health condition.