Why an Aging Workforce and Demographic Shifts Could Impact Stock Markets—and Aetna Employees' Retirement

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'Understanding demographic trends, like the Middle-Old ratio, can offer invaluable insight for Aetna employees planning for retirement, as it highlights the potential for slower stock market growth in the future and suggests strategic adjustments to portfolios to align with shifting global economic conditions.' – Michael Corgiat, a representative of The Retirement Group, a division of Wealth Enhancement.

'By recognizing the impact of demographic shifts, such as the Middle-Old ratio, Aetna employees can better position their retirement portfolios to navigate upcoming market changes and demographic-driven economic shifts, helping their retirement planning to remain resilient in the face of long-term trends.' – Brent Wolf, a representative of The Retirement Group, a division of Wealth Enhancement.

In this article, we will discuss:

1. The impact of demographic shifts, particularly the Middle-Old ratio, on stock market trends and retirement planning.

2. How population changes influence market cycles and economic growth, with a focus on Aetna employees.

3. Strategies for adjusting retirement portfolios based on demographic forecasts, including exposure to emerging markets.

The long-term outlook for stock markets and retirement planning is being affected by the demographic changes happening in the United States and other industrialized nations. The 'Middle-Old ratio' (M/O ratio), which analyzes the ratio of middle-aged to elderly individuals, is a key factor that investors, particularly Aetna employees, should consider when planning for the future. For those preparing their retirement plans over the next decade or more, this ratio offers a unique approach to forecasting long-term stock market trends.

The Effect of the M/O Ratio on Stock Markets

The M/O ratio is determined by dividing the number of individuals aged 40 to 49 by the number of people aged 60 to 69. This metric has shown a strong correlation with long-term stock market cycles, especially in the S&P 500. Research conducted by Alejandra Grindal, chief economist at Ned Davis Research, has revealed that shifts in the M/O ratio often coincide with significant highs and lows in the stock market. ¹

For example, in 2000, when the internet bubble burst and the 1990s bull market reached its peak, the M/O ratio reached its highest point. This marked the end of an era of rapid economic growth and stock market gains. Following this peak, the ratio began to decline, mirroring the 2008 global financial crisis and the subsequent bear market. Since the middle of the 2010s, the M/O ratio has been rising, indicating that a shift may be on the horizon within the next decade.

It is essential to note that while the M/O ratio may act as an indicator for long-term market trends, it is not useful for forecasting short-term market movements. For instance, it did not signal the steep market declines in 2022. Nevertheless, it remains a valuable tool for understanding the cyclical nature of the stock market.

The Influence of Demographics on Stock Market Cycles

John Geanakoplos, a professor at Yale University, has made significant contributions to understanding the relationship between financial markets and demographics. His 2002 study highlighted that many of the boom-and-bust cycles in the stock market since World War II can be attributed to shifts in population composition, particularly the proportion of middle-aged versus elderly individuals. ²  Geanakoplos explained that stock markets tend to rise when a significant portion of the population is in their prime working years and decline when a larger share of the population is elderly and no longer contributing to the economy.

This demographic shift is driven by the relative sizes of different age groups, not just the overall population. While some may focus on population growth when forecasting economic outcomes, it is the relative sizes of the middle-aged and senior cohorts that most significantly impact stock market performance.

It is expected that the M/O ratio will continue to rise into the 2030s. However, it will begin to decline again around the mid-2030s, which may signal a slowdown in stock market growth. This long-term pattern suggests that investors, particularly those at Aetna preparing for retirement, should be ready for potentially weaker equity returns starting in the early 2030s.

Taking Demographic Trends into Account When Managing Your Retirement Portfolio

Anyone preparing for retirement, especially Aetna employees with a long investment horizon, should understand how demographic shifts influence stock markets. This information can help you adjust your portfolio to align with anticipated market conditions, particularly if you are more than ten years away from retirement. As the M/O ratio seems to be peaking, it may be time to consider reducing exposure to U.S. stocks and reallocating to other regions, such as emerging markets.

For those nearing retirement, traditional strategies like those in target-date funds often recommend gradually decreasing equity exposure. For example, Vanguard’s target-date funds suggest a 30% allocation to U.S. stocks by the time an investor turns 65. However, due to demographic trends, a more cautious approach may be needed, especially for those in their 60s who wish to limit exposure to U.S. stocks.

Investors should also reevaluate the international component of their portfolios. While Vanguard's glide path recommends a 20% allocation to non-U.S. stocks, this may need to be adjusted based on the demographic outlook of specific countries. Over the next 25 years, developed nations outside the U.S. will also experience a decline in their M/O ratios, but not as sharply as in the U.S.

In the coming decades, emerging markets, particularly in Asia and Africa, are expected to see higher M/O ratios. As a greater portion of their populations enters middle age, these regions could experience economic expansion and market growth. To capitalize on these trends, it might make sense to increase your exposure to emerging markets, especially if you are nearing or already in retirement.

Conclusion: Preparing for Population Shifts and Stock Market Changes

Demographic trends, as illustrated by the M/O ratio, may influence stock markets and retirement planning. These trends indicate that starting in the early 2030s, investors, particularly those at Aetna with long-term horizons, may want to prepare for a period of potentially slower equity growth. As the middle-aged population reaches its peak, the stock market dynamics may shift, potentially leading to reduced returns in developed nations, including the United States.

To account for these anticipated demographic changes, it may be helpful to consider lowering your exposure to U.S. stocks and increasing your investment in emerging markets, where demographic trends appear more favorable. By adjusting your portfolio to reflect these long-term patterns, you can potentially position for a future with slower market growth and shifting global economic conditions. For a more sustainable retirement, begin planning now.

As the elderly population grows, the global workforce is shrinking, which could slow economic growth. A 2023 World Economic Forum report states that aging populations are contributing to a decline in the global workforce, potentially dampening economic productivity. This trend may lead to slower stock market returns and increased inflation, especially in developed countries where the aging population is advancing more rapidly.

Retirement planning must evolve as demographic changes and stock market patterns change. Understanding the M/O ratio and its implications could help you adjust your retirement portfolio, especially when considering opportunities in emerging markets. By aligning your investments with these demographic shifts, you can better prepare for a future where market growth may slow, supporting a more sustainable retirement.

Think of the stock market as a vehicle traveling along a winding road. For years, the car has been running smoothly, driven by a powerful engine (the large working-age population). But now, the engine is aging, and the fuel (economic growth and productivity) is running low. The aging population is like the car approaching a steep incline. Investors must adjust their speed, refuel with more strategic investments, and be ready for a slower journey into retirement.

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Sources:

1. Grindal, Alejandra. 'Why America's Aging Population Will Be a Problem for Stocks and Your Retirement.'  Morningstar , 2 June 2025.

2. Geanakoplos, John, Michael Magill, and Martine Quinzii. 'Demography and the Long-Run Predictability of the Stock Market.'  Brookings Institution , Jan. 2004, pp. 245–311.

3. Roberts, Stan. 'Why America's Aging Population Will Be a Problem for Stocks and Your Retirement.'  MarketWatch , 2 June 2025.

4. VanEck Research Team. 'Emerging Markets: Policy Uncertainty Tempers a Strong Start to 2025.'  VanEck , May 2025.

5. BlackRock. 'Five Forces Shaping Retirement.'  BlackRock , Feb. 2025.