Has Better Nutrition Driven Down Mortality Rates?

Before the COVID-19 pandemic struck in 2020, the world had experienced a steady decline in mortality for at least 60 years. We measure mortality using the crude death rate (CDR), which is the number of deaths divided by the population. The CDR for the entire world was 17.2 deaths per 1,000 people in 1960, and that rate decreased to 8.7 in 2021, according to data from the World Bank. However, that decline wasn’t uniform across the globe. For example, the U.K.’s CDR decreased from 11.5 to 9.7 during that period, and Chad’s rate fell from 26.3 to 12.5.

Declining Mortality and Improved Nutrition

One popular theory has suggested that declining mortality is due to improved nutrition. One way to study this is to examine the relationship between caloric intake, which measures the average consumption of calories per person per day, and CDR. The idea is that as more people in a country increase their caloric intake, there would be fewer people who die from starvation, thus yielding a negative relationship between nutrition and mortality. The theoretical link between nutrition and mortality was intended for poor economies as they undergo the process of economic development from a stage of undernourishment and starvation to higher standards of living.

The connection between nutrition and mortality has been investigated in historical contexts. For example, Thomas McKeown’s 1976 book, The Modern Rise of Population, concluded that the steady decline in mortality in the 20th century was related to the increase in food supplies, which meant better nutrition. But a 1983 article by Massimo Livi-Bacci argued against this relationship by showing that the British peerage and the general population had identical life expectancies despite the peerage having access to better nutrition.

In this post, we look at post-World War II data to study whether nutrition differences across countries can account for mortality differences.

Example of Nigeria

One way to see whether the theory holds is by looking at specific countries over time. For example, consider Nigeria. In the figure below, we see that country’s caloric intake (shown on the left y-axis) and the CDR (shown on the right y-axis) of Nigeria from 1961 to 2020. If the theory is valid, then when caloric intake increases, CDR will decrease.

The Evolution in Caloric Intake and Mortality in Nigeria

SOURCES: Food and Agriculture Organization and World Bank’s World Development Indicators.

NOTE: Average daily caloric intake is measured as kilocalories per day.

Before 1985, the average caloric intake in Nigeria was about 1,850 calories, which is generally under the recommended level of caloric intake of 2,000 to 3,000 calories. When Nigeria was undernourished, CDR was declining: It fell from 26 in 1961 to around 19 in 1981. Then around 1985, caloric intake started to increase for the next 10 years. During this time, CDR did not change and remained rather flat. Then starting in the late 1990s, the average caloric intake leveled off at around 2,600 calories, but we see a steady decline in CDR, which declined to about 11 by 2020.

Thus, the time series data for Nigeria suggests that there is no strong link between nutrition and CDR.

A Cross-Country View

We can also test the theory by looking at many countries at a point in time. In the figure below, we illustrate the relationship between caloric intake and CDR in 2010 for 170 countries. Each point on the scatter plot represents a different country. The broad sample includes low-income countries such as Afghanistan and high-income countries such as Germany.

The Relationship between Caloric Intake and Mortality in 2010: A Cross-Country Look

SOURCES: Food and Agriculture Organization, World Bank’s World Development Indicators and authors’ calculations.

NOTES: The dotted red line is the trend line, which shows a correlation of -0.12. Average daily caloric intake is measured as kilocalories per day.

As the figure shows, the relationship appears to be flat. That is, countries with vastly different caloric intakes, ranging from less than 2,000 to more than 3,500, have the same CDR; countries with roughly the same caloric intake, say 2,700, have different CDRs.

Both the time series and cross-section evidence suggest that there does not exist a strong relationship between nutrition and mortality. The decline in CDR is not necessarily a result of caloric intake, which means that there are other important factors to account for the decline in death rates. While increased nutrition can help people live better lives, it does not always lead to a decline in mortality for a country as a whole.