Originally written Spring 2023 – Post was sitting in my drafts. I’ll start publishing more soon even though they are rough drafts! Will edit them into final drafts over time (not static).

Each year, the scientific research around Vitamin D grows. New insights into the steroid hormone’s various regulatory roles in maintaining healthy human physiology continue to be discovered. One role is that and mood regulation, in particular seasonal depression.

Research have tried to pinpoint which chemical is responsible for the shifts in mood. However prime suspects melatonin and Vitamin D have both been shown to be no different in SAD patients vs controls. Certain neurotransmitters however, have been showed to be altered, although the root cause has yet to be described. While studies have shown that Vitamin D levels aren’t lower in SAD patients than controls, those patients have been shown to have a greater hypersensitivity to light and a few studies have reported efficacy in treating SAD with high dose vitamin D. While light therapy has been shown to be effective in SAD, adjunct therapy with vitamin D supplementation may increase the chance of remission.

Could it be possible that SAD patients have a high baseline requirement for Vitamin D? In the studies that compared them and controls, the levels were slightly lower, albeit not significantly. To be fair, it is more likely that depending on genetics, certain individuals require greater baseline vitamin D levels. It has already been shown that person can different in the rate at which they produce Vitamin D and melatonin. Also, individual differences in BMI, metabolism, and certain drug interactions may affects vitamin D status.

In this review I have listed each clinical trial done to date including patients with SAD and that also involve vitamin D supplementation. From my perspective, the results show that vitamin D supplementation is effective only in doses no less than 10,000 international units with regards to SAD.

Current recommended daily allowance by US regulatory bodies is 100-200ug/day. Considering the average 10,000-25,000iu produced through daily UVB (direct) sun exposure^1,2, this value seems quite low. Several scientific articles have been published in recent years challenging this reference range, exposing it as being critically low. Current upper limits, or maximum dosages listed by health officials are 200-300iu. The main concern referenced in exceeding upper limit guidelines is hypercalcemia. Since Vitamin D is co-absorbed with calcium, you can understand the concern. Luckily, studies on high-dose vitamin D rarely see this phenomena. Case studies and very early research using unsafe levels of vitamin D >100,000/day did indeed cause hypercalcemia, so caution must be taken. Levels of >40,000iu per day was deemed as the safe upper limit in a 1999 review¹.

Seasonal Depression’s prevalence is associated with latitude. The more north or south of the equator you live, the less sunlight you’ll get throughout the year. X et al showed this trend in 19XX. Unfortunately, Y et al cause a stir when their study did not show the association, however, I have examined the latitiude ranges of both studies and it seems that Y did not include a wide enough range to capture the obvious association (see diagram).

Vitamin D deficiency or sub-clinical insufficiency has a prevalence of 75% of the adult US population. Reasons for the large number are many and include: too much time spent indoors, overuse of sunscreens, chronic use of UVB shielding clothing and accessories (sunglasses), and over-reliance on food sources of Vitamin D. Common official US health systems mention Vitamin D from food sources in the recommendations to meet daily requirements. However, I’ve done a quick dive into the numbers, and the amount of food you would have to eat to get enough Vitamin D speaks for itself!

To clarify, all Vitamin D referenced in this article is meant to refer to the D3 form. Also remember that common units for Vitamin D are either iu (international units) or mcg (micrograms). (2,000iu = 125mcg) Be advised any person considering supplementing with vitamin should consult with their doctor first. Also, if the intake is extraordinarily high, signs of hypercalcemia should be monitored for…

Several scientific reports have been published which account borderline mega-dose vitamin D having significant benefits. These mega or “breakthrough” doses may be required to overcome the hormonal insufficiency at the root of several medical conditions. I hope by writing this article I can grab the interest of prospective clinical trial professionals interested in investigating the potential and build on safety data for vitamin-D mega doses. These are just a few examples of many studies showing vitamin D safe upper limits of no less than 10,000 international units.²

2019: 5,000 to 50,000iu/day in 4,700 patients. No adverse events or hypercalcemia.

2016: 7,143 to 14,288iu/day in 282 patients.² Safe and no effect on calcium levels.

2013: 35,000 iu/day + Low calcium diet (i.e no dairy, fortified milks, etc.) in 25 patients. -> No change in calcium, safe and effective.

I think 5k iu per 50lb of weight daily for SAD in fall winter moths would help a lot of people.

References

1. McCullough P et al. Daily Oral Dosing of Vitamin D3 Using 5000 to 50,000 International Units a Day in Long-term Hospitalized Patients: Insights From a Seven Year Experience. Journal of Steroid Biochemistry and Molecular Biology. May, 2019: Vol 189.
2. Jetty V er al. Safety of 50,000-100,000 Units of Vitamin D3/Week in Vitamin D-Deficient, Hypercholesterolemic Patients with Reversible Statin Intolerance. North American Journal of Medical Science. March 2016: Vol 8(3).
3. Finamore D et al. A Pilot Study Assessing the Effect of Prolonged Administration of High Daily Doses of Vitamin D on the Clinical Course of Vitiligo and Psoriasis. Dermatology and Endocrinology. March 2013: Vol 5(1).