Hello! In our last lesson, we defined Polycystic Ovarian Syndrome (PCOS) and traced the history of its diagnostic criteria. We saw that the shift from the strict 1990 NIH criteria to the broader 2003 Rotterdam criteria changed how many women could be diagnosed with the syndrome. This historical context is essential for today's topic.
This lesson addresses the second learning outcome in our module on PCOS fundamentals: Describe the global epidemiology and prevalence of PCOS across different populations. We will explore how common PCOS is around the world, a field of study known as epidemiology. You will learn that answering the simple question "How common is PCOS?" is surprisingly complex, precisely because of the different diagnostic criteria we discussed previously. We will investigate the key factors that cause prevalence rates to vary, including ethnicity, geography, and lifestyle.
1. The Big Picture: Global Prevalence of PCOS
Let's start by getting a general sense of the numbers. PCOS is recognized as the most common endocrine disorder in women of reproductive age, but the exact prevalence figures you encounter can vary.
Polycystic Ovary Syndrome (PCOS) | Overview of Associated Conditions, Diagnosis & Treatments
These two short clips from videos we've seen before provide slightly different top-line prevalence estimates. This illustrates the challenge we'll be exploring.
First, watch this clip from JJ Medicine, from 00:40 to 00:56, and note the prevalence range he gives.
14. Polycystic Ovarian Syndrome ( PCOS ) : Obstetrics and Gynaecology Lecture
Now, let's watch this clip from MedSchool Simplified for a different perspective.
Watch from 00:52 to 01:10 and note the statistic provided here.
As you saw, one source estimates a prevalence between 5-15%, while the other states it could be as high as 20% (one in five women). Why such a wide range?
The answer lies in the complexity of epidemiological studies for PCOS. The reported prevalence depends heavily on three main factors:
- The diagnostic criteria used (e.g., NIH vs. Rotterdam).
- The population studied (e.g., ethnicity, geographic location).
- How the study sample was selected (e.g., women from a fertility clinic vs. the general population).
A recent, large-scale analysis using data from the Global Burden of Disease (GBD) study provides one of the most comprehensive modern estimates.
Global burden of polycystic ovary syndrome among women of childbearing age, 1990–2021
This paper, 'Global burden of polycystic ovary syndrome,' uses a massive dataset to analyze trends. Let's read the introduction to get the most current global figures and understand the study's scope.
Read the 'Background' paragraph and the first paragraph of the 'Introduction'. Focus on the overall prevalence range, the total number of cases estimated in 2021, and the percentage increase since 1990.
This paper confirms the general range of 5-21% and provides a staggering figure: 65.77 million prevalent cases worldwide in 2021. Critically, it also highlights that the global burden of PCOS is increasing, with the number of cases rising by 89% between 1990 and 2021. This demonstrates that PCOS is a significant and growing public health concern.
2. Why Prevalence Varies: A Deeper Look
Now let's break down the reasons for the wide variation in prevalence estimates.
a) The Impact of Diagnostic Criteria
As we learned in the last lesson, the Rotterdam criteria are less strict than the NIH criteria. This directly impacts prevalence rates. A study using Rotterdam criteria will almost always report a higher prevalence in the same population than a study using NIH criteria.
The image below provides a powerful visual summary of how prevalence changes depending on the criteria applied in different parts of the world.
For example, look at the purple region (Australia). A landmark study there found that using NIH criteria resulted in a prevalence of about 8.7%, but using the broader Rotterdam criteria in the same group of women yielded a prevalence of 11.9%. This single example perfectly illustrates the impact of the definition on the numbers.
b) The Influence of Ethnicity and Geography
PCOS does not affect all populations equally. There are significant differences in both the prevalence and the presentation (the specific symptoms) of PCOS among different ethnic and geographic groups.
Polycystic Ovary Syndrome: An Updated Overview ...
This systematic review, 'Polycystic Ovary Syndrome: An Updated Overview,' is specifically designed to explore these differences. We will read through its findings, which are conveniently organized by region.
First, read the 'Abstract', the main 'Introduction' (up to Figure 1), and the short paragraph under the heading '3.2. Epidemiology in Different Ethnicities'. This will set the stage by confirming the importance of ethnicity and geography.
Now let's examine the specific data for different populations, as detailed in the same article.
Polycystic Ovary Syndrome: An Updated Overview ...
Let's continue with the same paper to see the specific prevalence rates reported across the globe.
Please read the sections '3.3. Prevalence in Europe, America, and Australia,' '3.4. Prevalence in Iran,' '3.5. Prevalence in Asia,' and '3.6. Prevalence of PCOS in India.' As you read, look for the following key points: Prevalence rates in European countries like Spain and Greece. The difference in prevalence between Mexican women in Mexico and Mexican-American women. The very high prevalence reported in Indigenous Australian women. General characteristics of PCOS in East Asian vs. South Asian women. Specific prevalence rates in India and the comparison between urban and rural populations.
Let's summarize those key findings:
- Caucasian Populations (Europe, Australia): Studies in Spain, Greece, and Australia (using NIH criteria) show prevalence rates clustering around 6.5% to 8.7%.
- Hispanic Populations: Studies show a higher prevalence among Mexican-American women in the US (13%) compared to women in Mexico City (6.6%), suggesting environmental and lifestyle factors play a role.
- Asian Populations: There is significant diversity within Asia.
- East Asians (e.g., Chinese, Japanese) tend to have a lower prevalence of hirsutism but may have a higher risk of metabolic issues at a lower BMI. The prevalence in China was reported at 5.6%.
- South Asians (e.g., from India, Sri Lanka) tend to have more severe symptoms, including higher rates of hirsutism, insulin resistance, and metabolic complications. The prevalence in Sri Lanka was 6.3%.
- Indian Populations: Given your background in Ayurveda, the data from India is particularly relevant. Studies have found that prevalence is higher in urban areas compared to rural areas, likely due to differences in diet and sedentary lifestyles. Stress was also identified as a contributing factor.
- Indigenous Populations: Indigenous Australian women show a very high prevalence of around 26%, along with higher rates of obesity and type 2 diabetes, which has been linked to a shift away from traditional lifestyles.
Test your understanding!
A researcher conducts a PCOS prevalence study in a rural Chinese village and reports a rate of 5%. Another researcher studies an urban population of South Asian immigrants in the UK and reports a rate of 15%. Both used the Rotterdam criteria.
Based on what you've just learned, propose two distinct factors that could help explain this threefold difference in prevalence.
Show answer
Several factors could explain the difference:
- Ethnicity: We learned that East Asian women (Chinese) tend to have a lower prevalence of some PCOS features compared to South Asian women, who often have a more severe presentation and higher rates of metabolic issues that can contribute to the syndrome.
- Environment and Lifestyle: The urban UK population likely has a more sedentary lifestyle and a different diet compared to the rural Chinese village. The article on global prevalence mentioned that urban living is associated with a higher risk of PCOS, likely due to these lifestyle factors. The "thrifty phenotype" hypothesis, which we will discuss later, suggests that some ethnic groups are more susceptible to metabolic diseases when transitioning to a Western lifestyle.
c) The Role of Socio-Demographic Factors
Lifestyle and environment are closely tied to socio-economic development. The Global Burden of Disease study analyzed this link using the Socio-Demographic Index (SDI), a composite score of a country's income, education level, and fertility rate.
Global burden of polycystic ovary syndrome among women of childbearing age, 1990–2021
Let's return to the GBD paper to understand how a country's development level relates to its PCOS burden.
Please read the sections 'SDI regional level' and 'Association between PCOS burden and SDI'. Focus on the overall relationship between SDI and prevalence, and note the distinction between the total number of cases (highest in middle SDI regions) and the rate of disease (highest in high SDI regions).
The findings show a complex but clear pattern:
- There is a positive correlation between SDI and PCOS prevalence. As a country's socio-economic development increases, its reported prevalence of PCOS tends to rise. This may be due to better diagnostic capabilities, higher awareness, and lifestyle factors associated with developed nations (e.g., diet, sedentary behavior).
- The highest rates of PCOS are found in high-SDI countries.
- However, the largest absolute number of cases and the most significant increase in prevalence are seen in middle-SDI countries. This suggests these transitioning nations are at the epicenter of the growing PCOS epidemic.
Conclusion
In this lesson, we moved from defining PCOS to understanding its scale as a global health issue. You now have a detailed picture of its epidemiology.
Key Takeaways:
- PCOS is a very common condition, with a global prevalence estimated between 5% and 21%, affecting over 65 million women.
- The global burden of PCOS has been steadily increasing over the last 30 years.
- Prevalence estimates vary widely due to several key factors:
- Diagnostic Criteria: Broader criteria like Rotterdam lead to higher prevalence figures.
- Ethnicity & Geography: Prevalence and symptoms differ significantly across populations, with South Asian and some Indigenous populations showing higher risk and severity.
- Socio-Demographic Factors: Higher levels of socio-economic development are associated with higher prevalence rates, likely due to lifestyle factors and better diagnosis.
Preview of the Next Lesson:
We have repeatedly seen how central the diagnostic criteria are to both defining and counting PCOS cases. The 2003 Rotterdam criteria are the most widely used standard in the world. Therefore, in our next lesson, we will perform a deep dive to master them. We will break down each of the three components—hyperandrogenism, oligo- or anovulation, and polycystic ovarian morphology—so you understand precisely what they mean and how they are assessed in a clinical setting.