Outdoor air pollution contributes to weaker bones, concludes a new study of more than 3,700 people living on the outskirts of Hyderabad.

India is home to 22 of the world’s 30 most polluted cities, where air quality crises are frequent and breathing-related health problems are on the rise.

The average age of study participants was 35.7; natural bone loss begins during the 30s, but researchers say the loss of bone mineral content in participants’ spines and hips — standard locations where bone strength is measured for osteoporosis diagnosis — is above and beyond normal loss associated with aging, or bone loss due to lifestyle risk factors for osteoporosis, such as lack of dietary calcium, insufficient physical activity, smoking, and more.

The study authors even controlled for exposure to indoor air pollution, as from biomass cooking fuels, concluding that general outdoor air pollution contributes to weaker bones. Specifically, for every additional exposure to 3 micrograms per cubic meter of PM2.5 (the smallest and most dangerous type of airborne particulate matter), both men and women experienced an average loss of 0.011 grams of bone mineral density per square centimeter in the spine and 0.004 g/cm2 in the hip.

How, exactly, air pollution affects bone health is unclear — researchers posit pollution may prompt inflammation and an imbalance in free radicals and antioxidants that damages bones. The real discovery here, they say, is the strong association between rising pollution and lost bone mass; explanations will come later, with additional research.

“What we see overall is a quite consistent pattern of lower bone mineral content with increasing levels of air pollution,” study author Cathryn Tonne, of the Barcelona Institute for Global Health, told New Scientist. It’s the most rigorous study to date to establish air pollution’s effect on bone health; the few previous studies on the topic have been inconclusive.

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Poor bone health has major health implications, especially for people with female physiology living in polluted metros. Over time, enough bone loss can lead to osteoporosis, when the creation of new bone — a constant process — can’t keep up with bone loss — also a constant process, especially from age 30 onward. Osteoporosis is a condition of skeletal fragility so extreme that even mild stress, as from coughing or bending, can cause a bone to fracture or break. While osteoporosis has many contributing factors — ranging from lifestyle factors like those above to hereditary factors — people with female biology are more at risk for osteoporosis because they experience menopause, which is characterized by a drop in the body’s level of estrogen, a hormone that provides protection against bone loss. They’re also more likely to experience thyroid problems, have eating disorders, have autoimmune disorders, and lead more sedentary lifestyles — all risk factors for osteoporosis.

While osteoporosis — already on the rise in India — is associated with old age, as bone loss accrues over decades, the new finding raises the possibility that diagnosis of the condition may skew younger in the coming years if efforts to improve air quality do not take effect. For this reason, people with female physiology may want to pursue the ways to prevent osteoporosis that are under their control, long before they probably ever expected to worry about the condition.

Ways to prevent osteoporosis (as much as possible)

The most effective way to avoid osteoporosis that is under one’s control (one can’t do anything about a family history of the condition, for example) is to maintain an active, healthy lifestyle, starting in one’s 20s. This includes not smoking, limiting alcohol intake, and avoiding excess intake of salt and caffeine, all of which can inhibit calcium absorption. Healthy eating and weight-bearing exercise (which could be anything from walking to weight training) also keep bones strong and help maintain a healthy body weight — which in turn together help avoid osteoporosis. And consider discussing vitamin D and calcium supplementation with a doctor. Deficiencies of vitamin D, which helps the body absorb calcium, are widespread in India, and intake of calcium, the mineral responsible for bone strength, has been declining in Indian diets over decades.

Discussions about bone strength and ways to prevent osteoporosis with a doctor become all the more critical for individuals with diabetes, autoimmune disorders, thyroid problems, depression, and/or gastrointestinal disorders, as these conditions and/or the medication for them can weaken bones.

For people with female physiology 40 and older, the recommendations on how to avoid osteoporosis change as perimenopause and menopause set in.

“The number of osteoporotic fractures is expected to increase considerably over the next decades, particularly for non-Western populations,” forecast the authors, in the new study. Putting the time in sooner, rather than later, on the factors under our control can help us not figure among the stats.