Are you taking enough vitamin D to ward off the winter blues?

As daytime light rapidly diminishes, side-effects may start to emerge around the holiday season. Low light exposure leads to a decrease in vitamin D production. Vitamin D deficiency is common in those with seasonal affective disorder, known as SAD.

SAD is a type of depression that may include symptoms of, fatigue, low motivation, loss of interest in activities, difficulty sleeping, changes in appetite or weight and difficulty concentrating.

The recommended daily dose of vitamin D is 400-800IU, yet for many, this dose fails to elevate levels sufficiently due to genetic variations. Vitamin D is a fat-soluble steroid hormone that relies on several genes for proper production, transport, and receptor binding, respectively known as CYP2R1 (vitamin D 25-hydroxylase), GC (vitamin D-binding protein), and VDR (vitamin D receptor). Variations within these genes are associated with vitamin D deficiency. This means that individuals who carry these variants are more likely to develop vitamin D deficiency when their vitamin D intake is low, such as during the winter months with low sunlight exposure.

  • CYP2R1 – vitamin D 25-hydroxylase
  • GC – vitamin D-binding protein
  • VDR – vitamin D receptor

While the recommended daily dose of vitamin D is a guideline for the general public, these levels fail to account for individual needs as a result of genetic variations. Clinical trials show that there are quite significant individual variations in response to dose. In a study with 1787 participants given 1000IU of vitamin D for a year, individuals with genetic variations in CYP2R1 and VDR had a 4% decrease and up to 3% increase of vitamin D levels per allele. This dose is above the recommended dose of 400-800IU.

This highlights two important factors, 1) the need to test (your genes and vitamin D levels) and 2) the need for individual dosing. It is not enough for most people to take 1000IU or even 2000IU of vitamin D. Vitamin D is a hormone and nuclear factor that modifies not only mood but immunity, hormone balance and bone health. It is important to say the least. Talk to your healthcare provider if you are experiencing any symptom of SAD and get tested. It is a simple step that you can take to preserve your mental health and improve your quality of life during the upcoming months.


  1. Barry, Elizabeth L., et al. “Brief Report: Genetic Variants in CYP2R1, CYP24A1, and VDR Modify the Efficacy of Vitamin D3 Supplementation for Increasing Serum 25-Hydroxyvitamin D Levels in a Randomized Controlled Trial.” The Journal of Clinical Endocrinology and Metabolism, vol. 99, no. 10, Oct. 2014, p. E2133.


Dr. Robyn Murphy, ND
Scientific Advisory Board Member