Research shows that 92% of women of childbearing age in Beijing have vitamin D deficiency, with only 1% maintaining healthy levels, according to a 2026 study of 2,325 women. Vitamin D levels dropped significantly during winter months and were lower in younger women, suggesting that women planning pregnancy should get tested and consider supplements, particularly during darker seasons.
A new study of over 2,300 women in Beijing found that nearly all women of childbearing age don’t have enough vitamin D in their blood. According to Gram Research analysis, 92% of women showed vitamin D deficiency, with only 1% having healthy levels. The problem got worse during winter months and affected older women more than younger ones. Doctors are now recommending that all women planning to get pregnant should get their vitamin D levels checked and consider taking supplements to support their health and their future babies’ development.
Key Statistics
A 2026 cross-sectional study of 2,325 women in Beijing found that 92.47% had vitamin D deficiency, 6.24% had insufficiency, and only 1.29% had sufficient vitamin D levels.
According to Gram Research analysis of this 2026 study, women aged 35 and older had significantly higher serum 25-hydroxyvitamin D concentrations compared to women under 35, with the lowest levels observed during winter months.
The 2026 Beijing study revealed a mean serum 25-hydroxyvitamin D concentration of 34.45 nmol/L among 2,325 women of reproductive age, indicating widespread deficiency in this population.
The Quick Take
- What they studied: How much vitamin D women of childbearing age have in their blood, and whether the amount changes with the seasons or their age
- Who participated: 2,325 women aged 18-49 in Beijing, China who came for health checkups before trying to get pregnant between December 2022 and December 2024
- Key finding: Nearly 9 out of 10 women (92.47%) didn’t have enough vitamin D, while only 1 out of 100 had healthy levels. Vitamin D levels were lowest in winter and higher in older women
- What it means for you: If you’re a woman planning to have children, getting your vitamin D checked and taking supplements if needed could be important for your health and your baby’s development. This is especially important during winter months
The Research Details
Researchers looked back at blood test results from women who came to a health clinic in Beijing for checkups before trying to get pregnant. They collected data over two years, from December 2022 through December 2024. The women were divided into two age groups: those under 35 years old and those 35 and older. They also organized the results by season (spring, summer, fall, and winter) to see if the time of year made a difference in vitamin D levels.
Vitamin D levels in the blood were measured using a standard test called serum 25-hydroxyvitamin D. The researchers then classified each woman’s vitamin D status into three categories: deficiency (not enough), insufficiency (somewhat low), or sufficiency (healthy amount). They compared the results between age groups and seasons to find patterns.
This type of study is called a cross-sectional study, which means researchers took a snapshot of vitamin D levels at one point in time rather than following women over months or years. This approach is good for understanding how common a problem is in a specific population.
Understanding how common vitamin D deficiency is among women planning pregnancy is important because vitamin D plays a key role in bone health, immune function, and fetal development. By looking at real data from a large group of women, researchers can identify who needs help and when they need it most. The seasonal patterns are especially important because they show that women might need extra vitamin D support during winter months.
This study included a large sample size of 2,325 women, which makes the findings more reliable. The study used standard medical definitions for vitamin D levels, so the results are comparable to other research. However, because this was a retrospective study (looking at past records), researchers couldn’t control all the factors that might affect vitamin D levels, such as diet, sun exposure, or supplement use. The study was conducted in one city in China, so results might be different in other locations or countries with different climates and populations.
What the Results Show
The study found that vitamin D deficiency is extremely common among women of childbearing age in Beijing. Out of 2,325 women tested, the average vitamin D level was 34.45 nmol/L, which is considered low. The breakdown was striking: 92.47% of women had deficiency (not enough vitamin D), 6.24% had insufficiency (somewhat low), and only 1.29% had sufficient levels (healthy amount).
When researchers compared age groups, they found an important difference. Women aged 35 and older had significantly higher vitamin D levels than women under 35. This might seem surprising, but it could be because older women spend more time outdoors or have different lifestyle patterns.
Seasonal changes made a big difference in vitamin D levels. Women tested during summer months had higher vitamin D levels than those tested in winter. This makes sense because sunlight helps our bodies make vitamin D naturally. Winter months showed the lowest vitamin D levels across all groups, suggesting that women need extra support during darker months.
The study confirmed that vitamin D deficiency is not just a minor issue but a widespread health concern in this population. The fact that only 1.29% of women had healthy vitamin D levels suggests this is a systemic problem affecting nearly everyone. The combination of age and seasonal effects means that younger women during winter months are at highest risk for severe deficiency.
Previous research has shown that vitamin D deficiency is common in many populations, especially in areas with less sunlight or where people spend less time outdoors. This Beijing study confirms those patterns and adds important information about women of childbearing age specifically. The findings align with other studies showing that vitamin D deficiency is particularly common in East Asian populations and in winter months across all regions.
This study looked at women in one city in Beijing, so the results might not apply to women in other parts of China or other countries with different climates. The study didn’t collect information about women’s diets, sun exposure, or whether they were already taking vitamin D supplements, which could all affect the results. Because researchers looked at past records rather than following women over time, they couldn’t determine whether vitamin D levels stayed the same or changed for individual women. The study also only included women who came for preconception health checkups, so it might not represent all women of childbearing age.
The Bottom Line
Women of childbearing age, especially those planning pregnancy, should ask their doctor to check their vitamin D levels. If levels are low, vitamin D supplementation is recommended. This is particularly important during winter months or for women who spend limited time in sunlight. The evidence for this recommendation is strong based on this large study of over 2,300 women.
All women of childbearing age should care about this, especially those planning to become pregnant. Women living in areas with long winters or limited sunlight should be particularly attentive. Women over 35 may have slightly better vitamin D levels naturally but should still get tested. Men and children may also benefit from vitamin D assessment, though this study focused on women.
Vitamin D supplementation typically takes 4-8 weeks to meaningfully raise blood levels. However, women planning pregnancy should ideally start checking and supplementing several months before conception to ensure optimal levels during early pregnancy, when vitamin D is especially important for fetal development.
Frequently Asked Questions
How common is vitamin D deficiency in women trying to get pregnant?
Very common. A 2026 study of 2,325 women found 92% had vitamin D deficiency. Only 1% had healthy levels, suggesting nearly all women planning pregnancy should get tested and likely need supplementation.
Does vitamin D change with the seasons?
Yes, significantly. Research shows vitamin D levels are lowest in winter and highest in summer. Women need extra attention to vitamin D intake during darker months when natural sun exposure is limited.
Why is vitamin D important before pregnancy?
Vitamin D supports bone health, immune function, and fetal development. Low levels during pregnancy are linked to complications. Getting adequate vitamin D before conception helps ensure healthy levels during early pregnancy when the baby’s development is most critical.
Should older women worry about vitamin D differently than younger women?
Somewhat. The 2026 study found women over 35 had higher vitamin D levels than younger women, but both groups showed widespread deficiency. All women of childbearing age should get tested regardless of age.
How much vitamin D supplement should I take?
This depends on your individual test results and your doctor’s recommendation. Typical supplementation ranges from 1,000-4,000 IU daily, but your healthcare provider should determine the right dose based on your blood levels and health status.
Want to Apply This Research?
- Track your vitamin D supplementation daily and log your sun exposure minutes (outdoor time between 10am-3pm). Set a reminder to retest vitamin D levels every 3 months, especially tracking changes between seasons.
- Set a daily vitamin D supplement reminder in your app. During winter months, increase outdoor time by 15-30 minutes daily when possible. Log which foods you eat that contain vitamin D (fatty fish, egg yolks, fortified milk) to track dietary intake alongside supplements.
- Create a seasonal tracking pattern: test vitamin D levels in early winter and early summer to understand your personal seasonal variation. Log supplement adherence daily. Track any symptoms like fatigue or bone pain that might correlate with vitamin D status. Share results with your healthcare provider to adjust supplementation as needed.
This article summarizes research findings and should not replace professional medical advice. Vitamin D levels and supplementation needs vary by individual. Women of childbearing age should consult with their healthcare provider about vitamin D testing and appropriate supplementation, especially those planning pregnancy. This is particularly important for women with specific health conditions, those taking medications that affect vitamin D absorption, or those with dietary restrictions. Always discuss any new supplements with your doctor before starting, as excessive vitamin D can be harmful.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.