Why do hot flashes remain a medical mystery?

It’s 3:05 in the afternoon, and I’m working at my desk when I start to get an uncomfortable prickly heat sensation. Within 30 seconds, my body temperature goes from its normal range (35.8 to 36.4 degrees Celsius) up to 36.8 degrees. My face reddens, my pulse increases from my normal 53 beats per minute to 59. I’m breathing faster and harder, and sometimes I even feel breathless. I may have to stop what I’m doing because of a sudden lack of energy. I may feel light-headed and even nauseated. At about 40 seconds in, the heat starts to subside as I break into a sweat. My skin from my scalp to my ankles is bathed in perspiration. By one and half minutes, it’s all over. But if the room is cool, the sweat may leave me feeling clammy and chilled.

Hot flashes happen day and night. On a good day, I might have about 12 hot flashes that cause only a light sweat. On a bad day, I can have more than 30 hot flashes and be so drenched in sweat that I need to change clothes and take extra showers. I’m lucky that I usually sleep through the night sweats or awaken only momentarily – many women suffer insomnia because of night sweats.

I am one member of the first generation of women to go through menopause without hormone replacement therapy (HRT), which was used to help women from the World War II to the baby boom generations avoid menopausal symptoms. Widespread use of HRT stopped after studies showed it raised the risk of some types of cancer as well as heart disease. Nevertheless, some women I know who are really suffering with symptoms are taking bioidentical hormones for a few years; it works well for some women and less well for others.

Estimates say 70% to 80% of menopausal women will have hot flashes (rates vary by country), and a recent study says they last seven and a half years on average, much longer than previously thought.

While this is mainly a women’s problem, some men also experience hot flashes as their hormone levels drop during “andropause.” My father had them during a therapy for prostate cancer that lowered his androgen hormone levels.

So, this is an almost-universal natural process. You would think that we would understand why it happens. But here’s the thing – medical knowledge really does not know why menopause causes hot flashes. For example, the Mayo Clinic website states: “The exact cause of hot flashes isn’t known.” Most medical sources explain that your estrogen level drops and then you have vasomotor symptoms, but stop short of explaining the mechanism leading from one to another. Because they don’t know.

There are a few teams working on research into the mechanism, and I’m eager to hear from them, because maybe research could shed a little light on how to cope with them.

Because there’s another ugly little fact: most of the advice well-intentioned health care professionals give to menopausal women about hot flashes has little evidence to back it up. And some of it is completely wrong.

Here is typical advice, from WebMD.

“To prevent hot flashes, avoid these triggers:

  • Stress
  • Caffeine
  • Alcohol
  • Spicy foods
  • Tight clothing
  • Heat
  • Cigarette smoke

Other things you can do to keep hot flashes at bay include:

  • Stay cool. Keep your bedroom cool at night. Use fans during the day. Wear light layers of clothes with natural fibers such as cotton.
  • Try deep, slow abdominal breathing (six to eight breaths per minute). Practice deep breathing for 15 minutes in the morning, 15 minutes in the evening and at the onset of hot flashes.
  • Exercise daily. Walking, swimming, dancing, and bicycling are all good choices.
  • Try chill pillows. Cooler pillows to lay your head on at night might be helpful.”

Let’s start with caffeine. While a 2005 study found some evidence that caffeine triggers hot flashes, a 2010 study found only a small effect of caffeine on hot flashes (this study included caffeinated sodas and cocoa). However, a very well-conducted 2011 study found that “women who drank more coffee had less severe [hot flashes] than the ones who drank less coffee.” I’m not seeing a lot of reasons to avoid caffeine, and coffee may actually help (in fact, I find that it provides short-term relief).

Which brings me to alcohol. The 2010 study found only a small effect of alcohol on hot flashes, and the 2011 study found no effect of alcohol drinking. A study just out showed that drinking alcohol during menopause actually decreased the chance of having hot flashes at all, as well as their severity. Alcohol is associated with health and social problems, so I wouldn’t start or increase drinking because of hot flashes, but there is no evidence that you should avoid alcohol if you are currently a moderate drinker.

Deep, slow abdominal breathing: This is a new approach being tested; results are not yet available. It may help cope with a hot flash. The jury is out on whether it could prevent hot flashes or make them less severe.

Anything that heats you up: Warm clothing, warm weather, warm beverages, warm food… basically anything warm can bring on a hot flash. One of my friends can get a hot flash walking by a hot stove. Keeping the room cool, turning on a fan or air conditioner, sleeping with fewer covers, etc. can all prevent hot flashes or make them less severe. But not entirely. You are still going to get them.

Tight clothing: I could find absolutely no evidence for this. The fact that women loosen or take off their clothes during hot flashes is just to get cool.

Spicy food: I found one study that came out in 2013 showing that a diet with regular hot spicy food intake increased hot flashes. The odd spicy dish might bring on a hot flash just because it warms you, but I wouldn’t cut out spicy food if it’s not a big part of your diet.

Cigarette smoke: I found mention of one study that found second-hand smoke increases hot flashes in non-smokers. More important is the evidence on smoking, which is conflicting. Observational studies have shown a negative effect of smoking, but that could be due to other positive health behaviour among non-smokers. The 2011 study, which had a strong design to detect triggers, found no effect of smoking. A new study shows that quitting smoking has a positive effect on hot flashes, making them less frequent and less severe, and that hot flashes were worse among women who had smoked than among non-smokers. Quitting smoking is a good idea for many reasons, and there is some limited evidence that it helps with hot flashes.

Obesity: Many studies have shown that obesity is a risk factor for hot flashes, so losing weight will help those who are really overweight. Women with a healthy weight should not try to lose weight to help with hot flashes – there’s no evidence for this. Furthermore, one study found that fasting (empty stomach) worsened hot flashes, and glucose improved them, so make sure you are not going hungry.

Stress: A 2005 study found that feeling happy and in control actually increased hot flashes, and stress decreased them. A small controlled study conducted in Japan and published in 2008 showed that doing a difficult mental task increased hot flashes on the spot. A recent study found that greater perceived stress and more depression and anxiety symptoms when hot flashes started were associated with more years of hot flashes. However, these stress symptoms may be an effect rather than a cause, and depression and anxiety are also symptoms of menopause itself. Limiting stress is a good idea for lots of reasons, but it’s unclear whether it helps with hot flashes. And I’m not going to stop doing difficult mental tasks because they might cause hot flashes.

Exercise: A very good randomized controlled trial published this year showed that exercise had no effect on hot flashes. A previous study showed that exercise actually worsened hot flashes, unless it was intensive exercise, in which case it improved them. Exercise is good for your general health, and there are lots of reasons to get exercise, but it probably won’t help with hot flashes.

The problem with trying to study hot flashes is that there are strong placebo effects – basically, if you think something might help, it probably will, but it seems to be mind over matter. And hot flash frequency and severity change often during menopause, sometimes day to day, so it’s difficult to say that doing any particular thing affected hot flashes. That’s why anecdotal reports from women that something improved their hot flash experience are unfortunately unreliable. The lifestyle advice has very little evidence behind it, except for losing weight if you are obese and for quitting smoking. Help for hot flashes will come from basic research into what causes them – I’m waiting for that news.

3 thoughts on “Why do hot flashes remain a medical mystery?

  1. I agree with your description of your hot flashes. Mine are very similar, except that a precursor to mine is that I actually get about 5 seconds of “chest heaviness”, where I have to stop and catch my breath, and then I mentally prepare myself for the hot flash, which comes as you described it, within a few seconds of the chest heaviness. My heart rate also increases, and I have a moment of intense thirst. I am unable to take any type of hormones because of the risk of DVT, so I take magnesium throughout the day which helps a little bit. I really try not to get bent out of shape about all the hot flashes throughout the day and night. Logically I understand that it’s just a normal part of menopause, but emotionally, I would love to go through a 24 hour period where I am not faced with searching for a cool air vent and the wish to tear off my clothes and drink a river. Ugh…..I have at least 4 more years to go if the average amount of time that they last is 7.5 years…

  2. Hi Carolyn,
    Interesting post! I am not surprised that much of the advice isn’t backed up by science. I am interested though in what you mentioned when you said the rates vary in different countries. I’m wondering if hot flashes could be related to diet, like so many things are. Have you seen any research on this? By the way I think I will get to meet you at the conference in Guelph.
    Laurie Gough

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