Tummo Meditation: What Harvard’s Herbert Benson Measured in Monks

Tibetan Monks’ Tummo Meditation: What Harvard’s Herbert Benson Measured

Can a meditating monk really warm his own body in freezing air? Yes, within limits. In 1981 a Harvard cardiologist named Herbert Benson measured three Tibetan Buddhist practitioners of g-tummo, the "inner heat" meditation, and found that they could raise the skin temperature of their fingers and toes by as much as 8.3 °C. A study published in 2013 confirmed that the practice can also lift core body temperature. What the research does not show is anything supernatural. It shows how far a trained human body can steer processes most of us leave on autopilot.

Below is what tummo is, what Benson and later researchers actually recorded, which popular claims went too far, and what an ordinary reader can reasonably take from it.

What tummo meditation is

Tummo (written gtum mo in Tibetan) is usually translated as "inner fire" or "fierce woman," a name that also refers to a fierce goddess of heat. It belongs to Vajrayana, the tantric form of Buddhism practised in Tibet, and it is the first of the Six Yogas (or Six Dharmas) of Naropa, a set of advanced practices that the other five build upon.

In the traditional teaching, the practitioner combines breath retention low in the abdomen with detailed visualisation of channels and a flame at the navel. The heat is meant as a by-product. The stated aim is spiritual: to calm and gather the mind so that it can rest in the recognition of emptiness. Teachers such as Tsongkhapa, the 14th–15th century master, advised beginners to practise gently, without forcing the breath, and under a qualified teacher.

Stories of hermits who spent Himalayan winters in thin cotton robes, sometimes called repa (cotton-clad ones), circulated for centuries. Those stories are what drew Western scientists to the monasteries in the first place.

What Herbert Benson measured

Benson was already known for The Relaxation Response, his 1975 book describing the calming physiological changes produced by simple meditation. After meeting the Dalai Lama, who reportedly welcomed the research, he took his instruments to India to test the more extreme claims.

The fieldwork took place in February 1981 in Upper Dharamsala, home of the Tibetan community in exile. Three monks who had practised tummo daily for about six years were studied in unheated stone buildings. Thermometers on their fingers, toes, navel and lower back recorded the changes as they meditated. The results were published in the journal Nature in 1982:

One monk's finger rose by 5.9 °C and his toe by 7 °C during a session of just under an hour.
A second raised his finger by 7.2 °C and his toe by 4 °C.
The third showed a smaller finger rise of about 3.2 °C but a toe rise of 8.3 °C.

Benson concluded that the most likely mechanism was vasodilation: the monks were widening the small blood vessels in their hands and feet, sending more warm blood to the skin. That is something the body normally does on its own, not on command.

The short film above, widely shared as "Superhuman Abilities of Himalayan Monks," mixes archival footage with later retellings, so treat its numbers with the caution explained below.

Wet sheets, frozen ledges and a slower metabolism

The most famous images come from later expeditions, summarised in an April 2002 article in the Harvard Gazette. According to that account, monks in a northern Indian monastery sat in a room kept at about 40 °F (4.5 °C) while assistants draped sheets soaked in 49 °F water over their shoulders. Instead of shivering, the meditators produced visible steam, and each sheet was reported dry in roughly an hour. Each monk dried three sheets over several hours.

How #monks use #meditation to raise their #body #temperature. #WorldHealthDay @DeepakChopra https://t.co/krtTRlDtth pic.twitter.com/3kHpBRUYCm
— Buzzworthy (@thebuzzworthyco) April 7, 2016

The same report describes a February 1985 night in which monks slept on a rocky ledge about 15,000 feet up in the Himalayas, with air near 0 °F, wearing only shawls. They reportedly fell asleep quickly, did not huddle together, showed no visible shivering, and walked back to their monastery at dawn. In Sikkim, Benson's team also recorded a drop in metabolism, measured by oxygen use, of up to 64 percent. For comparison, the article notes that metabolism falls only about 10 to 15 percent during sleep and around 17 percent in ordinary meditation.

These accounts are striking, but they deserve two cautions. First, they come from a news write-up rather than a full peer-reviewed paper describing every measurement. Second, critics later pointed out that steam rising from a wet sheet in a cold room proves only that the body is warmer than the air around it, which is true of anyone. The sheet-drying demonstration is memorable; the thermometer readings are the stronger evidence.

What later research added

In 2013 a team led by cognitive neuroscientist Maria Kozhevnikov, then at the National University of Singapore, published a study in the journal PLOS ONE that set out to repeat Benson's work with modern equipment. It broadly confirmed the warming effect and went further by measuring core body temperature, not just the skin.

The researchers separated two parts of the practice. A forceful "vase breathing" technique, with strong breath holds, raised core temperature into the range of a slight to moderate fever. A gentler breathing style, together with the visualisation of inner fire, helped practitioners hold that elevated temperature for longer. The study also found that Western volunteers with no tummo experience could produce some warming with the breathing alone, which suggests the technique is learnable rather than a special gift. The authors proposed that the heat may help meditators reach deep meditative states, rather than being only a side effect.

Images like the one above, of a young monk apparently hovering in an alley, are staged or edited photographs. They spread alongside the tummo research, but nothing in the studies involved levitation.

Meditation and the brain: two related lines of research

The tummo experiments are often bundled together with brain studies of experienced meditators, which explains why the online versions of this story tend to blur them.

Zoran Josipovic, a researcher at New York University who is also a longtime meditation practitioner, used functional MRI to look at monks and other experts. The brain is often described as running two broad networks: one that engages with external tasks and a "default mode" network that becomes active during self-reflection and mind-wandering. They usually work like a seesaw. Josipovic reported that some expert meditators could keep both networks active at once during a form of non-dual awareness, which he linked to the feeling of oneness that practitioners describe. This is preliminary work on small groups.

At the University of Wisconsin–Madison, neuroscientist Richard Davidson and his colleagues studied Tibetan Buddhist practitioners with tens of thousands of hours of practice. Their work, including a well-known 2004 paper on unusually strong gamma-band brain activity during compassion meditation, helped popularise the idea that sustained mental training changes the brain, a property known as neuroplasticity. Most of these studies involve small numbers of highly unusual practitioners, so their results are best read as early findings.

Buddhist Monks have known for thousands of years what science is just now learning https://t.co/KTwON4Uhc5 #meditation #science #Buddhist
— Miloš Takač (@milostakac) April 4, 2016

Myths that grew around the studies

"Monks raised their temperature by 17 degrees." The documented maximum in the 1982 paper was 8.3 °C at the toes. The larger figure seems to come from mixing Fahrenheit and Celsius, or from unclear reporting of where the measurement was taken. A rise of 8.3 °C is about 15 °F, which may explain the "15 degrees" version that also circulates.

"Harvard proved monks have superhuman powers." The research described a trained physiological skill. The monks were influencing blood flow, heat production and oxygen use through breathing and attention, which is impressive and still entirely biological.

"Anyone can safely try this in the snow." The traditional teaching insists on a teacher and gradual training. Forceful breath-holding techniques can cause dizziness or fainting, and cold exposure can cause hypothermia. Never practise breath-holding in or near water, and if you have a heart condition, high blood pressure, epilepsy or are pregnant, talk to a doctor before trying any intense breathing method.

What it means for the rest of us

Benson's own interest was practical. He argued that a large share of doctors' visits in the United States involve stress-related complaints and hoped that mind-body methods could stand beside medicine as part of self-care. He was careful to say the extreme feats needed years of training; the everyday lesson was that even simple meditation measurably calms the body.

That message holds up. Regular, modest practice, such as slow breathing, a body scan or a few minutes of focused attention each day, is a reasonable way to manage everyday stress for most people. It is a complement to medical care, not a replacement for it. The monks of Dharamsala are a reminder of how responsive the body is to the mind, and of how much patient, unglamorous practice lies behind that kind of control.

Sources: Harvard Gazette: Meditation changes temperatures (April 18, 2002); Snopes: Harvard study and Tibetan monks' body temperature; Wikipedia: Tummo. Opening and levitation photos: original photographers unknown.

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