Does melatonin cause weight gain?

The short answer is no. In fact, melatonin may well do the opposite.

Melatonin is an incredibly important hormone that all human bodies produce so that we can sleep.

 It is the hormone that is activated by darkness (that is, night time), and your levels of melatonin should reduce with daylight, at around the time you usually get up.

But, there are also synthetic versions of this hormone which can be taken as supplements or medicine.

People most commonly take the supplement when they are jet-lagged or when their melatonin levels are lower due to factors like old age or anxiety.

But, the supplement may have other benefits as well.

Melatonin can help regulate your body temperature, your blood pressure, the levels of some of your hormones, and it can reduce dopamine – which helps to keep you awake.

It may also help with weight loss.¹

Melatonin’s impact on weight loss

Various studies have demonstrated that melatonin may be used for obesity control.

One recent study, conducted on diabetic rats, for example, found that melatonin increased the amount of brown adipose tissue (BAT) mass, which is the “good” fat that your body uses, rather than stores.

The impact of that was a reduction of white visceral fat in the abdominal region – that is the fat that can cause the most negative impact on your health, since most of your organs are in that region.²

The same study found that melatonin can positively impact thermogenic activity and mitochondrial mass and function.

Thermogenesis is when your body burns calories in order to produce heat, and mitochondria are cell structures (organelles) which are involved in thermogenisis.³

The rats that were studied experienced these changes regardless of their levels of activity (exercise) or their diets.

However, for humans, doctors do recommend that any melatonin treatment should be complementary to a healthy and well-balanced diet and a good amount of exercise.⁴

Other studies have demonstrated that melatonin tablets can have an impact on metabolism.

One study looked at menopausal women. Menopause is a time when people find it even harder to lose body fat and gain muscle. The study found that melatonin can impact hormones like leptin, adiponectin, and insulin levels. Together, these hormones are involved in regulating your body’s metabolic processes, including fat burning and glucose use.⁵

The impact of melatonin on sleep and weight

Apart from these direct impacts that melatonin tablets can have, there is also a correlation between a good night’s sleep and a healthy weight, and melatonin can also potentially help you get that quality sleep.

If you are not sleeping well, that can make you more susceptible to stress, and vice-versa.

This stress makes it harder to stick to a new diet, or feel motivated to exercise (though you really want to try to, if you can, as that also helps reduce stress and it helps you to get a good night’s sleep).⁶

If you are sleep-deprived, you are also more likely to make impulsive food decisions. When you are tired during the day, you are more likely to want the instant energy boost of carbohydrates or the feel-better boost of sugar.⁷

We also know that restricted amounts of sleep (less than seven hours a night, depending on your age and depending a bit on each individual), leads to people being more likely to develop obesity. 

Regularly getting less sleep than you need is associated with increased levels of ghrelin, salt retention and inflammatory markers.

Ghrelin is the hunger hormone that increases your appetite. Less sleep can also lead to decreased levels of leptin and insulin sensitivity.⁸

Finally, studies have also shown that when you are sleep deprived, your eCB levels may increase and be amplified.⁹

Endocannabinoid, or eCB, is a neurotransmitter which is associated with making you crave foods that are really palatable. That could be junk food for instance, or carb-heavy foods.

Of course, sleep deficiencies are just one of many factors that can contribute to weight gain or difficulties losing weight.

That is why weight loss, if that is something that is important to you (for health reasons or aesthetic reasons, energy levels, ability to sleep, or any other reason), often requires a holistic shift in lifestyle, ranging from diet, to exercise, to mental health, and even bed-time habits.

Last updated: 18 March 2021