Depression Patient friendly summary

 Major depressive disorder, commonly referred to as depression, is a mental disorder where extreme feelings of sadness can last for months, or even years.

Major depressive disorder (MDD) is known by many names, though it is most commonly called depression. Depression is a mental disorder where extreme feelings of sadness persist for many months or years, thus it is different from the feelings of sadness that we all feel from time to time.

People who are depressed have an extremely low mood and low self-esteem. They lose interest in activities they once enjoyed and tend to withdraw from others, unable to shake their feelings of hopelessness and despair.

Risk factors

  • The causes of depression are not well understood, but seem to involve both genetics and environment.
  • Those who are obese have a higher risk for depression.
  • Those diagnosed with diseases such as cancer, cardiovascular disease, and multiple sclerosis may develop depression.

Sunlight exposure and risk of depression

There are no reported studies linking ultraviolet-B (UVB) light to risk of depression. However, the symptoms of depression may intensify during the winter - what is known as Seasonal Affective Disorder (SAD).

Vitamin D and depression

 Low vitamin D levels may be related to depression rather than contributing to the disorder.

A number of studies report some connection between vitamin D levels and the risk of depression. Low vitamin D levels may be related to depression rather than contributing to the disorder. In addition, an increased risk of depression may be related to several vitamin D–sensitive diseases. For example:

  • Elderly Dutch community residents with minor or major depression had vitamin D blood levels that were 14% lower than residents without depression.
  • Italian women with lower vitamin D levels - less than 20 ng/mL (50 nmol/L) - had twice the risk of developing depression. For Italian men, the risk was increased 60%.
  • Postmenopausal women with one vertebrae fracture had 20% more depressive symptoms than women without a fracture. Women with at least three vertebrae fractures had three-fold the rate of depression compared to women without multiple fractures. Low vitamin D levels are an important risk factor for vertebral fracture.
  • Syrian women with heart disease, high blood pressure, or kidney disease were three times more likely to have depression. Syrian men with rheumatism and respiratory disease had an even greater risk of depression. There is good evidence that low vitamin D levels are a risk factor for all of these diseases.
  • A lifetime history of depression may be a risk factor for later development of Alzheimer's disease. Depression may increase the risk of mild cognitive impairment that turns into Alzheimer's. Patients with Alzheimer’s and depression have more pronounced hallmarks of the Alzheimer’s brain than patients with Alzheimer’s who are not depressed. Studies indicate vitamin D deficiency may also be a risk factor in Alzheimer’s.
  • One study showed that, in the United States, vitamin D deficiency occurred more often in certain people. These people were African-Americans, living in cities, obese, and depressed. People with vitamin D levels below 20 ng/mL (50 nmol/L) had an 85% increased risk of depression compared to those with vitamin D levels greater than 30 ng/mL (75 nmol/L).

How vitamin D works

Vitamin D may lower the risk of depression by:

  • Reducing the risk of diseases that may trigger depression, such as cancer, cardiovascular disease, and multiple sclerosis.
  • Reducing the production of cytokines. Cytokines are proteins that increase inflammation and have been shown to be a possible risk factor for depression.


There are no reported studies showing that vitamin D supplements reduce the risk of depression. However, given the evidence, it is possible that vitamin D could have a positive effect on those who suffer from depression.

Based on studies of cancer, cardiovascular disease, and influenza, vitamin D levels above 40 ng/mL (100 nmol/L) may reduce the risk of depression.


 Treating vitamin D deficiency in people with depression may result in improvement in long-term health and quality of life.

According to a recent review, treating vitamin D deficiency in people with depression or other mental disorders may result in improvement in both long-term health and quality of life. Reports confirm that vitamin D has a positive affect on depression:

  • Women in Washington State increased their vitamin D levels to 47 ng/mL (118 nmol/L) by taking 5000 IU of vitamin D each day during the winter. In some of these women, their depressive symptoms lessened as indicated by the decrease in their scores on a depression test.
  • Overweight and obese Norwegian women took 20,000 or 40,000 IU per week of vitamin D and their symptoms of depression decreased. Their scores were also lower on a depression test.
  • Based on studies of other diseases, vitamin D blood levels of 40–50 ng/mL (100–125 nmol/L) appear to reduce the severity of depression.

Find out more...

Do you want to find out more and see the research upon which this summary is based?  Read our detailed evidence summary on depression.

Page last edited: 27 September 2011