Depression

Sunshine as an Antidepressant?

The link between vitamin D and depression

Posted Jan 20, 2020

Kmac/Shutterstock
Source: Kmac/Shutterstock

Like all vitamins, vitamin D is integral to several bodily functions. It helps the body absorb calcium, which makes it important for bone health. Those who do not receive adequate levels of vitamin D may suffer from weak bones—a condition known as rickets in children and osteomalacia in adults—while older individuals may develop osteoporosis, which literally means “porous bone.”

Numerous products are fortified with it, including many cereals, milk, and even some orange juices, but it is still difficult to obtain all the vitamin D one needs through diet alone. Fortunately, vitamin D is also produced within our own body when our skin is exposed to ultraviolet B (UVB) radiation from the sun, which is why vitamin D is oftentimes known as the sunshine vitamin. Most people get the majority of their vitamin D through this process, especially in the summer when one only needs between 10 to 20 minutes of midday sunlight on one’s face and arms to produce all the vitamin D they need for the day.

Unfortunately, during the winter months, especially if one lives far from the equator (greater than 35 degrees latitude—roughly north of Atlanta), the sun becomes notably weaker and it can be difficult to obtain all the vitamin D one needs. This is especially the case for individuals with darker complexions, as they need a greater amount of strong sunlight to produce adequate levels of vitamin D.

One might think that this means that a glass of milk during the winter months can make up for the deficiency, but this is not entirely accurate. The recommended daily intake of Vitamin D is 600 IU (15 µg) for most people up to the age of 70, and 800 IU (20 µg) for individuals over the age of 70, but a glass of 8-ounce milk only contains around 100 IUs of Vitamin D. One would be better served regularly eating fatty fish, such as salmon, trout, tuna, and mackerel, as they contain more Vitamin D (a 3-ounce sockeye salmon fillet contains 450 IUs, for example). Mushrooms also contain a great deal of Vitamin D. Supplements are another option.

Apart from being integral to bone health, vitamin D is also important for muscles, nerves, the immune system, and cell growth, and some data suggests that a deficiency in vitamin D might be associated with certain types of cancers (particularly colon, prostate, and breast cancer), as well as other diseases. It may also play a role in mental health.

Vitamin D and the Brain

Though it is not clear that there is a correlation between vitamin D deficiencies and depression, some researchers have offered a potential, neurophysiological explanation for this association.

It is established that vitamin D receptors are found throughout the body and brain. Additionally, research has shown specificity to brain regions associated with the physiology of depression, most notably the prefrontal cortex, hippocampus, cingulate gyrus, thalamus, hypothalamus, and substantia nigra.

It has also been demonstrated that the active form of vitamin D, calcitriol, works to activate the gene expression of tyrosine hydroxylase, an enzyme that goes on to play a role in the synthesis of dopamine, epinephrine, and norepinephrine—three hormones that also can play the role of neurotransmitters in the brain. Disturbances of two of these chemicals, dopamine and norepinephrine, play a major role in depression. In fact, many antidepressants specifically aim to boost norepinephrine (and serotonin) by inhibiting its reuptake, thereby allowing for more norepinephrine to bind to available receptors.

Directionality

While this link initially seems compelling and could potentially explain a strong correlation between depression and vitamin D deficiencies, it has been difficult to demonstrate empirically that inadequate levels of vitamin D give rise to depression. On the one hand, reduced levels of calcitriol in the brain may not have that significant of an impact on the synthesis of dopamine, epinephrine, and norepinephrine, as there are other means of synthesizing these neurotransmitters. On the other, it has been difficult to establish the directionality of the correlation between vitamin D deficiencies and depression.

For example, a depressed person may lose their appetite and go outside less often than someone who is not depressed. Without taking a vitamin D supplement, these two behaviors will result in lower vitamin D levels and, over time, a vitamin D deficiency. This would mean that depression leads to inadequate vitamin D levels, not the other way around.

Conversely, studies have suggested that vitamin D deficiencies can affect the balance of two neurochemicals, serotonin and melatonin, which play a role in the regulation of one’s sleep-wake cycle (or circadian rhythm), thereby leading to sleep disturbances. Such sleep disturbances may result in negative effects on one’s mental health, as I noted in a previous post. Consequently, a vitamin D deficiency may make depression more likely if someone is prone to it.

Empirical Studies on Depression and Vitamin D

As Parker et al. noted in a 2016 analysis published in the Journal of Affective Disorders, there have been conflicting results when studying the association between depression and vitamin D. Some showed a positive association between low vitamin D levels and depression, while others did not find any compelling evidence linking depressive symptoms with deficient vitamin D levels. In some cases, vitamin D supplements improved depression scores, while it failed to do so in others.

The authors of the analysis found that many of the cross-sectional studies they examined failed to specify directionality, while the randomized controlled trials that evaluated vitamin D as a treatment for depression yielded inconsistent results. Additionally, the authors found that, in some cases, vitamin D in conjunction with an antidepressant was a more effective treatment than just the antidepressant alone, especially in instances where the patient had a vitamin D deficiency prior to treatment, which may have more to do with its improving the efficacy of the antidepressant than acting through an independent means.

Ultimately, more studies are needed to establish if there is in fact a positive association between depression and vitamin D deficiencies. However, this does not mean that one does not need vitamin D. The evidence is clear that Vitamin D is vital to bone health, and it is especially important for children and seniors to receive the recommended daily allowance with a combination of sunlight, diet, and, in some cases, supplements.

Dr. Ahmad reports no conflict of interest. He is not a speaker, advisor, or consultant and has no financial or commercial relationship with any biopharmaceutical entity whose product/device may have been mentioned in this article.