Sources of vitamin D include sunlight (ultraviolet B, or UVB, rays), dietary intake, and supplements.  Sunlight is the main source of human vitamin D.  Vitamin D refers to different forms of a steroid hormone.   Vitamin D3 (also called 1, 25-dihydroxycholecalciferol or calcitriol) is produced by the body when ultraviolet light (in the form of UV B) interacts with 7-dehydrocholesterol .  Vitamin D3 is thought to be more potent than vitamin D2, with D3 and D2 being the two forms of vitamin D contained in supplements.

Production generally occurs with natural sun exposure (particularly in seasons and latitudes with high UV indexes); some might occur from tanning beds, although tanning beds emit primarily UV A (Woo and Eide, 2010).  Light boxes filter out UV rays to deliver bright white light, and their mechanism of action is not thought to be related to ultraviolet light exposure (Lam et al, J Clin Psychiatry 2001).

Over the last decade, there has been increasing concern than many children and adults may not have sufficient levels of vitamin D.  For example, one study of childbearing women in the Northern U.S. found insufficient vitamin D levels in 54% of black women and in 42% of white women.  Certain people may be more vulnerable to being vitamin D deficiency, including those with greater skin pigmentation and those with less sun exposure (e.g., the elderly or those living in institutions).

Blood tests used to check vitamin D levels assay the active metabolite, 25-hydroxyvitamin D.   Different laboratories use different reference ranges, as well as different units of measurement.  In order to provide clearer guidelines regarding vitamin D deficiency and insufficiency, the Institute of Medicine (IOM) recently published new reference ranges for vitamin D levels.   A normal vitamin D level is greater than 75 nmol/L (or 30-60 ng/ml).  Less than 30 nmol/L (or 12 ng/ml) is considered deficient.  The IOM committee also notes that some, but not all, people may be at risk of vitamin D deficiency at levels from 30 nmol/L to 50 nmol/L (12-20 ng/ml).

Vitamin D and Depression

Most of the studies supporting the health benefits of vitamin D have been association studies (not treatment studies), where lower vitamin levels have been associated with certain adverse outcomes or diseases (e.g., breast cancer, hypertension, diabetes).  At this point, the benefits of supplementation with vitamin D for most indications have not been well studied.

Several, but not all, association studies have demonstrated a correlation between lower vitamin D levels and increased risk of depression (reviewed in Parker and Brotchie, 2011).  Higher dietary intake of vitamin D has been associated with a lower risk of depression in older women (Bertone-Johnson et al, 2011).

A prospective cohort study from Milaneschi and colleagues (2010) suggests a relationship between vitamin D levels and subsequent risk of depression.  In this study, including 531 women and 423 men who were 65 years of age or older, serum vitamin D levels were assessed at baseline, and after 3 and 6 years of follow-up.  The Center for Epidemiological Studies Depression Scale (CES-D) was used to assess mood, with a score of >16 used to identify depression.  Low vitamin D was defined as < 50 nmol/L.  Both women and men experienced a significantly greater risk of developing depressive symptoms with lower vitamin D levels, noting that the relationship was more robust in women (Hazard ratio of 2.0 in women and 1.6 in men).

There has not been adequate assessment of vitamin D as a therapy for major depressive disorder (MDD) or seasonal affective disorder (SAD).   In one treatment study, Jorde and colleagues (2008) assessed the impact of vitamin D supplementation on symptoms of depression in overweight and obese subjects (N=441); they used the Beck Depression Inventory (BDI) to assess depressive symptoms.  At baseline, lower vitamin D levels (<40 nmol/L) correlated with higher BDI scores.  The participants were randomized to Vitamin D (20,000 IU or 40,000 IU) or placebo per week for one year.  There was significant improvement in depressive scores among the two vitamin D groups compared to those receiving placebo.

In their review, Parker and Brotchie (2011) conclude that it is premature to make recommendations about Vitamin D for the treatment or prevention of depression.  They note that research assessing the role of vitamin D intake in terms of dietary intake is challenging, as the main source in the diet is fish, and results may be confounded by omega-3 intake which may also have a positive impact on mood.  They caution that a causal role for vitamin D deficiency in MDD or SAD is not established.  At this time, there is insufficient evidence to support its use for the treatment of MDD.  However, it is reasonable to check levels in those at risk for vitamin D deficiency, and to supplement for general health purposes (such as bone health) in individuals with depression.

Vitamin D and Perinatal Depression

Vitamin D deficiency appears to increase the risk of obstetrical complications.   Vitamin D levels have been reported to be inversely related to risk of gestational diabetes and poor glycemic control (McLeod et al, 2011).  Low vitamin D levels have also been reported to increase the risk of preeclampsia, although this has not been consistently demonstrated (Brannon and Picciano, 2011).

Bodnar and colleagues conducted an exploratory study and did not find that Vitamin D levels were related to risk of major depression during pregnancy (2011).  In another study, lower levels of vitamin D were associated with higher Edinburgh Postnatal Depression Scale (EPDS) scores in one postpartum sample (N=97) (Murphy et al, 2010).  Also of note is the fact that mothers with low vitamin D status secrete lower levels of vitamin D into the breast milk, putting exclusively nursing infants at risk of deficiency (Haggerty, 2011).  Therefore, it may be beneficial to assess vitamin D status in pregnant and lactating women, although impact upon depression risk is unclear at this time.

How Much Vitamin D Should You Take?

Of late, there has been some controversy regarding the adequate dosage of dosage of vitamin D.   The IOM committee has published recommendations for various age groups, reflecting scientific evidence for the health benefits of vitamin D.

 Recommended Dietary Allowance of Vitamin DMaximum Dosage of Vitamin D
Infants: 0 to 6 months 400 IU/day1,000 IU/day
Infants: 6 to 12 months 400 IU/day;1,500 IU/day
Children: 1-3 years600 IU/day2,500 IU/day
Children: 4-8 years600 IU/day3,000 IU/day
Age: 9-70 years600 IU/day4,000 IU/day
Adults: Over 71 years800 IU/day4,000 IU/day
Pregnant or Lactating Women600 IU/day4,000 IU/day

 

Most prenatal vitamins contain 400 IU of vitamin D.  Interestingly several recent studies showing the benefits of vitamin D in pregnancy used doses of 4,000 IU per day; however, most health groups recommend taking no more than 2,000 IU of the vitamin in supplement per day.  The risk of adverse events increases above 4,000 IU per day.

Both D2 and D3 are effective for raising blood levels of vitamin D, many experts recommend supplementing with vitamin D3, the form that is produced naturally by the body.  However, vitamin D3 supplements are typically derived from cod liver oil or lanolin and are therefore not vegetarian. If an individual has concerns about taking vitamin D3, vitamin D2 (which is plant-derived) can be an effective replacement.

Marlene Freeman, MD