Climate change effects: Heat waves and food insecurity weaken immune systems, study finds

05 Feb 2019 --- Heat waves can reduce the body’s immune response to the influenza virus, which could, in turn, have implications for how climate change may impact the future of vaccinations and nutrition, according to a new study from the University of Tokyo. The role that the heat plays in reducing nutritional intake may be a crucial reason behind the weaker immune response. The researchers recommend that nutritional supplementation is adopted in addition to appropriate vaccines in food-insecure communities.

Climate change has been predicted to reduce the yield and nutritional value of crops, as well as widen the range of disease-spreading insects. However, the effects of heat waves on immunity to influenza had not been studied previously, as the influenza virus is typically a winter-season disease.

The researchers housed healthy, young adult female mice at either a refrigerator-cold temperature (4°C or 39.2°F), room temperature (22°C or 71.6°F), or heat wave temperature (36°C or 96.8°F).

When infected with the virus, the immune systems of mice in hot rooms did not respond effectively. The step that was most affected by the high heat condition was the vital step between the immune system recognizing the influenza virus and mounting a specific, adaptive response.

How did the temperature affect nutrition?
Notably, mice exposed to a high temperature ate less and lost 10 percent of their body weight within 24 hours of being housed in the hot rooms.

Yet these mice could mount a typical immune response if researchers provided supplemental nutrition before and after infection with the flu virus. The supplemental nutrition included either glucose or short-chain fatty acids, chemicals naturally produced by intestinal bacteria.

In experiments at room temperature, researchers surgically connected mice, so that body fluids moved freely between underfed and normally fed mice, both infected with influenza. The fluids from normally fed mice prompted the immune systems of underfed mice to respond normally to the flu virus.

“Does the immune system not respond to influenza virus because the heat changes gene expression? Or because the mice don't have enough nutrients? We need to do more experiments to understand these details,” says Miyu Moriyama of the University of Tokyo.

The results may shed light on the commonality of getting sick once again while recovering from other illnesses.

“People often lose their appetite when they feel sick. If someone stops eating long enough to develop a nutritional deficit, that may weaken the immune system and increase the likelihood of getting sick again,” says Takeshi Ichinohe of the University of Tokyo.

The future of infection?
An important area of future study will be the effect of high temperatures on different types of vaccinations. Flu vaccines injected into the upper arm use an inactivated strain of the virus, but vaccines sprayed into the nose use live attenuated, or a weakened, virus.

“The route of delivery and the type of virus both may change how the immune system responds in high temperatures,” says Moriyama.

Until more research can clarify what these findings may mean for humans, Ichinohe and Moriyama cautiously recommend a proactive approach to public health.

“Perhaps vaccines and nutritional supplements could be given simultaneously to communities in food-insecure areas. Clinical management of emerging infectious diseases, including influenza, Zika and Ebola, may require nutritional supplements in addition to standard antiviral therapies,” says Ichinohe.

Furthermore, the researchers are planning projects to better understand the effects of temperature and nutrition on the immune system, including experiments with obese mice, chemical inhibitors of cell death and different humidity levels.

The threat from climate change is increasingly on the radar of a range of industries. It has been reccommened by the EAT-Lancet comission that a planetary diet be adopted in order to feed a growing population of 10 billion by 2050. While late last year the global debate around dietary changes was under the spotlight when some of the world’s leading science academies declared the global food system to be “broken,” claiming that it is failing and urgently needs to be turned around to avoid catastrophic climate change. An in-depth report from the InterAcademy Partnership (IAP) calls for a total transformation of how systems operate as agriculture and consumer choices are major factors driving “disastrous climate change.”