The Influence of Environmental Factors on Health

Every day, the environment around us quietly shapes our health in ways we may not fully realize. From the air temperature outside to the water flowing through our taps, environmental factors play a direct and measurable role in human well-being. Understanding these connections is essential – not just for scientists and policymakers, but for anyone who wants to make informed decisions about their health. This post breaks down four key environmental influences: climate and temperature, sunlight and UV exposure, water quality, and biotic factors like fungi and zoonotic diseases.

How climate and temperature affect human health 🔗

Climate variability is one of the most significant environmental drivers of health outcomes globally. As global temperatures rise, the frequency and intensity of extreme heat events are increasing at an alarming pace. The year 2024 was the hottest year on record, with global average temperatures exceeding 1.5 °C above the 1850-1900 average, and the ten years from 2015 to 2024 were the hottest decade ever recorded globally. This trend has direct consequences for human health.

Heat stress and cardiovascular strain 🔗

When temperatures climb beyond what the body can regulate, the result is heat stress – a condition where the body’s cooling mechanisms, primarily sweating, become overwhelmed. Heat stroke, the most serious heat-related disorder, occurs when the body can no longer control its temperature and the sweating mechanism fails, potentially causing death or permanent disability without emergency treatment. High humidity makes this worse because sweat evaporates more slowly, reducing the body’s ability to cool itself.

The cardiovascular system bears a heavy burden during extreme heat. The heart must work harder to pump blood toward the skin’s surface for cooling, which strains people who already have underlying heart conditions. A comprehensive analysis found that extreme temperatures are linked to 17 causes of death, primarily cardiorespiratory and metabolic diseases, with an estimated 1.7 million deaths worldwide associated with extreme temperatures in 2019 alone.

Vulnerable populations – including older adults, young children, outdoor workers, and people with chronic illnesses – face the greatest risk. Research from Yale School of Public Health found that heat-associated deaths in the United States rose by 53% over two decades, climbing from an annual average of around 2,670 between 2000-2009 to over 4,000 between 2010-2020. This increase reflects not just rising temperatures but also demographic shifts, including an aging population that is less resilient to environmental stressors.

Cold exposure and its health effects 🔗

While heat often dominates the conversation, extreme cold is also a major health threat. Cold weather constricts blood vessels, raises blood pressure, and increases the risk of heart attacks and strokes. Cold-related deaths in the U.S. rose from about 44,000 between 2000-2009 to more than 47,500 between 2010-2020, representing a 7% increase. Older adults, women, and individuals who are widowed or divorced are particularly vulnerable to cold-related illness.

Climate variability – with more frequent swings between extreme heat and extreme cold – means that communities must prepare for health threats at both ends of the temperature spectrum.

Sunlight and UV exposure: a double-edged sword 🔗

Sunlight is essential for life, but its effects on human health cut both ways. The same ultraviolet (UV) rays that help our bodies produce a critical nutrient can also cause lasting damage to the skin and eyes.

Vitamin D synthesis and its importance 🔗

When skin is exposed to sunlight, UVB rays interact with a protein called 7-DHC, converting it into vitamin D3 – the active form of vitamin D. This process is the primary natural source of vitamin D for most people. Vitamin D plays a vital role in maintaining bone health by regulating calcium absorption. Beyond bones, it supports immune function, muscle strength, and may help protect against certain cancers and autoimmune diseases.

Research estimates that over 50% of the global population is at risk of vitamin D deficiency, partly due to inadequate food fortification and the misconception that a healthy diet alone provides sufficient vitamin D. Deficiency can lead to rickets in children, and osteoporosis and increased fracture risk in adults. Several factors affect how much vitamin D the skin can produce, including skin pigmentation, age, latitude, time of day, season, and sunscreen use.

Skin cancer and UV-related damage 🔗

The same UVB wavelengths (290-320 nm) responsible for vitamin D production are also the primary cause of sunburn and DNA mutations that can lead to skin cancer. UVA radiation, the sun’s longer-wave rays in the 320-400 nm range, is a key driver of premature skin aging and also contributes to skin cancer development.

UV-induced immunosuppression – caused by both UVA and UVB exposure – is an important factor in skin cancer development. The three main types of skin cancer linked to UV exposure are basal cell carcinoma, squamous cell carcinoma, and melanoma. Of these, melanoma is the most dangerous, responsible for approximately 55,000 deaths globally each year. Geographic location matters: people living in areas with higher UV intensity face greater skin cancer risk, with squamous cell carcinoma showing the strongest correlation to cumulative sun exposure.

Striking the right balance 🔗

Strict sun-protection strategies to prevent skin cancer may inadvertently increase the risk of vitamin D deficiency, which itself carries serious health consequences. The key is finding a middle ground. Health organizations such as the American Cancer Society recommend getting vitamin D primarily through diet and supplements rather than unprotected sun exposure. People aged 1-70 are advised to get 600 IU of vitamin D daily, children under 1 need 400 IU, and adults over 70 should aim for 800 IU. Fatty fish, fortified milk, eggs, and mushrooms are all dietary sources.

For those who do get some sun, short periods of exposure (around 10-15 minutes) on less-protected areas of the body – outside of peak UV hours – may help support vitamin D levels without significantly increasing cancer risk. But the consensus among dermatologists and oncologists remains: use sunscreen, wear protective clothing, and rely on food or supplements for your vitamin D needs.

Water quality, pH levels, and health 🔗

Access to clean drinking water is a fundamental determinant of health. Two important aspects of water quality – its pH level and the presence of chemical contaminants – can have significant effects on the human body.

Understanding pH in drinking water 🔗

pH measures how acidic or alkaline a substance is, on a scale from 0 to 14 (7 being neutral). According to regulatory bodies such as the WHO and the U.S. EPA, the recommended pH range for safe drinking water is between 6.5 and 8.5. Water within this range is considered safe for consumption and has acceptable taste and mineral content.

When water pH drops below 6.5, it becomes acidic, soft, and corrosive – meaning it can leach metal ions such as lead, copper, and zinc from pipes into the water supply. Lead contamination is especially concerning. Even low-level lead exposure can harm children’s brain development and, in adults, increase the risk of high blood pressure and kidney damage. On the other hand, excessively alkaline water (above 8.5) can cause a bitter taste, mineral buildup in pipes, and may interfere with nutrient absorption in some individuals.

pH also affects the effectiveness of water disinfection. WHO guidelines recommend keeping water pH below 8 for chlorine-based disinfection to work properly. When pH rises too high, chlorine becomes less effective at killing harmful bacteria and viruses, compromising water safety.

Nitrate contamination and methaemoglobinaemia 🔗

One of the most serious water-quality-related health conditions is methaemoglobinaemia, commonly known as “blue baby syndrome.” This condition occurs when excessive nitrates in drinking water are converted to nitrites in the body, which then alter the iron in haemoglobin from its normal ferrous (Fe²⁺) state to the ferric (Fe³⁺) state. The resulting methemoglobin cannot effectively bind and transport oxygen, leading to tissue hypoxia – a dangerous reduction in oxygen delivery to the body’s tissues.

The connection between pH and methaemoglobinaemia risk is important: infants under six months have a higher gastric pH than adults, which allows bacteria to thrive in their digestive systems and convert more nitrate into nitrite. This makes them especially vulnerable. Nitrate contamination in water typically comes from agricultural runoff – fertilizers and animal waste – seeping into groundwater sources and private wells. Public water systems are monitored for nitrates, but private wells often are not.

The U.S. EPA has set a maximum contaminant level of 10 milligrams per liter (mg/L) for nitrate-nitrogen in public water supplies to protect against methaemoglobinaemia. Symptoms of the condition include headache, dizziness, shortness of breath, and a bluish discolouration of the skin (cyanosis). Severe cases can lead to seizures, coma, and death. Importantly, boiling contaminated water does not remove nitrates – it actually concentrates them as water evaporates.

Biotic factors: fungi and zoonotic diseases 🔗

Environmental health is not only shaped by physical and chemical factors. Biotic factors – living organisms in our environment – also pose significant health risks. Among the most important are pathogenic fungi and zoonotic diseases (infections transmitted between animals and humans).

Fungal threats to human health 🔗

The fungal kingdom includes at least 6 million species, of which approximately 625 have been reported to cause infections in vertebrates and about 200 are associated with human disease. Fungal infections range from superficial conditions (like skin and nail infections affecting an estimated one billion people) to life-threatening systemic infections in immunocompromised individuals.

Some of the most clinically significant fungal pathogens include Aspergillus species, which cause respiratory infections; Candida species, which can lead to systemic infections in hospitalised patients; and Histoplasma, which thrives in soil enriched with bird or bat droppings and causes lung infections when spores are inhaled. Fungal secondary metabolites known as mycotoxins – particularly aflatoxin produced by Aspergillus flavus on contaminated grain and peanuts – are linked to increasing numbers of liver cancers worldwide.

Climate change is making fungal threats worse. Global warming is driving the evolution of thermotolerance in fungi, allowing them to better adapt to human body temperatures, which leads to the emergence of humans as new hosts for previously harmless environmental fungi.

Zoonotic diseases: when animal infections jump to humans 🔗

Zoonotic diseases – caused by viruses, bacteria, fungi, and parasites – make up roughly 75% of all emerging infectious diseases. These infections can spread through direct contact with animals (bites, scratches) or indirectly through contaminated environments, food, or water.

Common zoonotic fungal infections include dermatophytosis (ringworm), which spreads easily between pets and humans; sporotrichosis, transmitted through contact with infected cats or contaminated plant material; and histoplasmosis, which can affect both humans and animals exposed to contaminated soil. According to the U.S. CDC, some fungal diseases like ringworm and sporotrichosis spread directly between animals and people, while others like histoplasmosis cause illness in both but do not transmit between them.

Several factors are accelerating the rise of zoonotic diseases. Urbanisation, deforestation, and the destruction of wildlife habitats bring humans into closer contact with animal populations, increasing the chances of disease transmission. The domestication of animals, population growth, global travel, and migration all contribute to the expanding reach of these infections. Additionally, the overuse of fungicides in agriculture is driving antifungal resistance, making some fungal infections harder to treat when they do reach humans.

The One Health approach 🔗

Addressing biotic health threats requires recognising the deep interconnection between human, animal, and environmental health – a framework known as One Health. This approach acknowledges that changes to the environment like warming temperatures, extreme weather events, and fungicide use all impact the risks and outcomes of fungal diseases. Effective surveillance of animal diseases, responsible use of antifungals, habitat conservation, and public health education are all essential components of reducing biotic health risks.

Why these environmental factors matter together 🔗

None of these environmental factors operate in isolation. Rising temperatures increase UV exposure and alter the geographic distribution of disease-carrying organisms. Climate change affects water cycles, which impacts water quality and contamination levels. Habitat destruction driven by development pushes wildlife – and their pathogens – into closer contact with human populations.

Understanding these interconnected risks is the first step toward building more resilient communities. Whether through improved water-quality monitoring, urban heat-island mitigation, responsible sun exposure practices, or investment in zoonotic disease surveillance, the tools to protect human health from environmental threats already exist. The challenge lies in deploying them effectively and equitably.

What do you think? Which environmental factor do you believe poses the greatest health risk to your community right now? And how well-prepared do you think your local health systems are to deal with the combined effects of climate change, water contamination, and emerging infectious diseases?

References

1. https://www.skincancer.org/blog/sun-protection-and-vitamin-d/
2. https://www.cancer.org/cancer/risk-prevention/sun-and-uv/sun-safety-and-vitamin-d.html
3. https://cdn.who.int/media/docs/default-source/wash-documents/wash-chemicals/ph.pdf?sfvrsn=16b10656_4
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC1247562/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5095550/
6. https://www.cdc.gov/fungal/about/one-health.html