The intensity of bipolar symptoms may change over time depending on a number of factors. Your treatment regimen, small or large changes in your life, and even the weather can impact bipolar disorder.

In fact, seasonal changes in the depressive and manic periods of bipolar disorder have been recorded and studied.

Bipolar disorder is chronic, and you may experience periods of remission as well as relapse. Knowing how the seasons and other environmental factors affect bipolar symptoms can help you and your loved ones manage better.

Bipolar disorder affects 1%-3% of the world’s population. It’s characterized by periods of mania or hypomania (high energy, grandiosity, disturbed sleep, reckless behavior, distractibility, sometimes psychosis) and periods of major depression.

The two “poles” of bipolar disorder — mania and depression — can each be impacted differently by seasonal changes.

Seasons and depression

You’re probably aware of seasonal affective disorder (SAD), which causes some people to experience depression during the colder, darker months of winter. SAD is a subtype of bipolar or major depressive disorder.

About 25% of people with bipolar disorder have seasonal affective disorder. An even more common condition is subsyndromal seasonal affective disorder, or seasonality. This is when mild depressive symptoms show up with changing seasons.

Causes of SAD include too little or too much sunlight and disrupted circadian rhythms, or sleep/wake cycles.

Seasons and mania

While lower levels of sunlight are associated with a depressed mood, sunnier days can affect the moods of people with bipolar disorder, too.

A 2018 study found that photoperiod — the period of time each day when a person is exposed to light — is a key element in bipolar disorder.

The 730-patient study showed that more people were hospitalized for mania in spring and summer when daylight exposure is highest throughout the year.

It also found that people with bipolar disorder were hospitalized for depression in winter when exposure to light is reduced due to shorter days.

Our circadian rhythms are powered by the suprachiasmatic nucleus in the brain. This part of the brain is concerned with regulating physiological circadian rhythms by detecting levels of sunlight and processing other environmental factors.

This regulation then triggers a range of processes in our bodies related to sleep, energy, hunger, and body temperature.

People with bipolar disorder have altered circadian and seasonal rhythms and sometimes demonstrate seasonal patterns of depressive and manic episodes. In a 2021 review of 51 studies, researchers found a few patterns:

  • Hospital admissions for bipolar depressive episodes peak in early winter.
  • Hospitalizations for manic episodes are more common in spring and summer.
  • Seasonal variations were more common in women with bipolar disorder.

Because people with bipolar disorder have disrupted circadian rhythms, things like shift work or travel across time zones can intensify bipolar symptoms. When circadian rhythms are “off,” you may experience sleep disturbances, altered hormones, and mood changes.

People with bipolar disorder are at a 20 to 30 times greater risk for suicidal behavior than the general population.

A 2021 analysis of data from 4,876 patients from 71 different geographic locations found that higher rates of attempted suicide were present in locations farther from the equator. These locations have more solar variation, meaning that the amount of radiation given off by the sun shifts drastically throughout the year.

Some studies indicate that sunlight exposure alone doesn’t explain seasonal variation in bipolar symptoms. Other environmental factors include ultraviolet exposure, temperature, weather, and light exposure early in life.

A recent study of people with bipolar disorder in Italy found that more people with bipolar disorder were admitted to the emergency psychiatric ward on days with higher temperatures and higher solar radiation.

In a 2016 analysis of more than 24,000 hospital admissions for mania in Denmark, researchers found there were higher admission rates on days with more sunshine, higher temperature, and less snow.

Bipolar disorder treatment aims to address both parts of the disorder. If you have bipolar disorder, your doctor will work with you to reduce both depressive episodes and manic episodes. You may be prescribed mood stabilizers or antipsychotic medication.

Regular medication may be taken alongside psychotherapy. Cognitive behavioral therapy (CBT) is one type of therapy that’s often used to treat depression and ongoing education about the disorder is recommended for recognizing mood changes and triggers.

Psychoeducation is another tool used to help people with bipolar disorder. Learning about the condition can help you recognize patterns of your symptoms and their onset. This awareness — and a self-care plan — can help with stress management.

Managing seasonal depression

Bright light therapy is recommended in the International Society of Bipolar Disorders as a treatment for acute bipolar depression, but clinical trials on the therapy are limited.

In one trial, 58 patients were given light therapy for 7 to 21 days, and 55% experienced remission of depressive symptoms by the end of treatment. Patients received light treatment using a lamp for 30 minutes during morning hours, the time when bright light is believed to have the best effect on depression.

However, two patients in the study experienced hypomanic episodes while undergoing light therapy. Light therapy has been under-researched in people with bipolar disorder because of concerns about triggering mania.

Talk with your doctor about whether light therapy could help with seasonal depression. It’s important to understand the risk of triggering a manic episode.

Managing seasonal mania

Less research has been done on treating seasonal or summer mania specifically, but understanding how the change of seasons may impact the disorder is a start.

Healthy sleep habits, consistency with doctor-prescribed medications, and stress reduction strategies can help prevent manic episodes that begin following a depressive period in winter.

Bipolar disorder symptoms can follow a seasonal pattern in 25% of patients. You may experience more depressive moods in the winter or darker months and be at higher risk for mania in the summer and spring.

Being aware of changes in your circadian rhythm and seasonal symptoms can help you and your healthcare professional manage bipolar depression.