A healthy dose of biodiversity

According to a recently published study, two hours in nature per week is a sufficient dose to produce health benefits. On the other hand, even a short excursion to natural environment has an immediate impact on well-being, as blood pressure, heart rate and stress hormone levels fall rapidly. The proper dose of nature is, however, probably not the same for everyone.

Published 6.8.2020
Writer: Jenni Lehtimäki

A home in close proximity to nature and trips in natural surroundings support human health and well-being. Studies show that blood pressure, heart rate and stress hormone levels fall rapidly in natural surroundings. There is a lot of recent information stating the health benefits of nature, but how much time is needed for receiving these benefits? It’s doubtful that there is a clear, unambiguous answer to this question.

I am especially interested in the benefits of nature during early childhood, when a child’s development is particularly sensitive to the effects of the environment. Events during childhood, and already during pregnancy, can affect one’s health later in life. A green home environment during childhood or life on a farm tends to protect against asthma and allergic diseases, which have greatly increased in Finland since the 1960s. I wonder whether a sufficient dose of nature in childhood would support one’s health later in life.

In my VIHERIKKUNA (“Greenwindow”) project, funded by the Sakari Alhopuro Foundation, I utilize data consisting of more than one million Finnish children to find out when exposure to nature is most impactful on children’s health. I believe there is a time window when it would be especially beneficial for children to be in touch with nature in order to promote long-term health. On the other hand, nature seems to have a dose-dependent effect, i.e., more contact with nature produces more health benefits. Consequently, the most effective health promotion could be to incorporate nature into everyday life in a more holistic way, throughout one’s lifetime.

Microbial diversity can be behind the health benefits of nature

In addition to the amount and time of one’s interaction with nature, the quality of the natural environment is important for health. Quality can mean numerous things, such as the ease of navigating an area or the level of biodiversity in a particular area. Biodiversity means all the diversity of life, from different individuals to different species and a wide variety of ecosystems. In both New Zealand and Australia, using extensive population data, it has been found that ecosystem diversity near the home protects children from asthma and allergic diseases. In the VIHERIKKUNA project, I examine whether ecosystem diversity close to the home also affects the health of Finnish children.

It is not yet clear to what extent the health benefits of nature are based on a lack of risk factors and, on the other hand, an abundance of protective factors. There is less air pollution and noise in nature than in built environments, but at the same time, people often get more exercise when out in nature, enjoy the sunlight, admire the beautiful scenery – and get exposed to environmental microbes. In my yet unpublished studies, I discovered that in rural Denmark, children were exposed to a number of microbes that were not present in Copenhagen at all. The functioning of the immune system of urban children was abnormal during early childhood as a result of the urbanization of microbes in their body. They also developed many more asthma and allergic diseases than children in rural areas. Indeed, the ever-increasing body of evidence suggests that microbial richness in nature may be one of the most significant factors behind the health benefits produced by nature.

An underutilized health promoter

According to the famous definition of the World Health Organization, human health consists of three parts: mental, physical and social health. Current research shows that nature promotes all three aspects and biodiversity further enhances the positive effect. In addition, a study of millions of people found that nature close to home reduced mortality by any cause. Thus, it is not an exaggeration to state that nature is an exceptional and completely underutilized health promoter that could have huge impacts on public health.

If there is a sufficient dose of biodiversity that supports human health, one should also ask how much biodiversity is needed to preserve itself. My research work is motivated by the valuable idea of my colleague Tari Haahtela: “If protection of biodiversity produces immediate health benefits, will environmental issues gain greater interest?” I hope that my research will both improve human health and provide a convincing argument for the promotion of nature conservation and a sustainable lifestyle.


Jenni Lehtimäki, PhD, is a Senior Researcher at the Finnish Environment Institute. In 2017, she defended her thesis on the biodiversity hypothesis regarding the relationship between two international megatrends, namely the loss of biodiversity and the increasing prevalence of non-communicable diseases, for the Faculty of Biological and Environmental Sciences of the University of Helsinki. She continues to study the subject and looks for practical ways to incorporate a healthy dose of nature into the daily lives of Finns.

Further reading:

Tari Haahtela: Lääkäri pohtii biodiversiteettiä. Medical journal Duodecim 2010;126(11):1364–5

Wikipedia page of biodiversity hypothesis