Tim,
The only information on preventing cluster headaches with vitamin D3 comes from data collected right here at CH.com, a similar thread on ClusterBusters, and an online survey of the Anti-Inflammatory Regimen.
To date, the primary thread at Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

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, has been viewed over 76,800 times with 1090 comments posted in the two years it's been running... At least 20% of the comments mine.
Data from from the online survey of the Anti-Inflammatory Regimen with vitamin D3 is proving to be very useful. That survey continues to collect data on efficacy, dosing, and lab results for 25(OH)D, calcium, and PTH (parathyroid hormone). This survey also collects demographic and epidemiological data.
It's not a gold standard RCT with A1 medical evidence. That said, the weight of the empirical evidence and first hand testimony on the effectiveness of this regimen collected from well over 250 cluster headache sufferers posting here at CH.com and over 70 participants in the online survey is significant.
So far, a preliminary compilation of the online survey results and tally of raw data collected here at CH.com are consistent. They're also in strong agreement that the efficacy of using the anti-inflammatory regimen as a CH preventative is 76% for episodic and chronic cluster headache sufferers (CH'ers) combined.
In addition, of the CH'ers who reported a favorable response to the anti-inflammatory regimen and who also had a lab test for 25(OH)D, the favorable responses occurred at 25(OH)D serum concentrations between 60 to 110 ng/mL. These responses occurred in as little as the first 24 hours to as long as two months after starting this regimen. Most CH'ers responded within the first two to three weeks.
What we're also starting to discover is why the other 24% of CH'ers who tried the anti-inflammatory regimen don't respond. Comorbidities involving liver, kidney, thyroid and parathyroid insufficiencies lead the list of likely suspects that interfere with the capacity of the anti-inflammatory regimen to prevent CH.
Viral infections and allergic reactions that challenge the body's immune system are also suspect, as are medical and dietary conditions that result in a lower than normal systemic pH.
There is information from formal studies on the pharmacokinetics and safety of vitamin D3 at the doses we're taking including the resulting 25(OH)D serum concentrations.
These studies were conducted by doctors and professors, most of whom are endocrinologists. The authors include names like Heaney, Veith, Hollis, Garland, French and Baggerly. These are the Jedi Masters of vitamin D3 Therapy.
Many of the studies they conducted and published employed a meta-analysis approach comprised of statistical techniques for combining results of multiple studies to obtain a quantitative estimate of the effect of vitamin D3 on 25(OH)D serum levels and overall safety.
When you combine data gathered here at CH.com, the survey data, and information from the formal studies of vitamin D3 above, it provides a compelling story of hope for cluster headache sufferers all over the world that a strong correlation exists between cluster headache and a vitamin D3 deficiency.
Moreover, when the vitamin D3 deficiency is treated with a regimen of vitamin D3, Omega 3 Fish Oil, and vitamin D3 cofactors, cluster headache symptoms either disappear completely or are significantly reduced to provide a good quality of life.
Again, this is not a gold standard RCT... but it appears we now have a safe, inexpensive and effective alternative treatment to prevent cluster headaches, as opposed to taking the standards of care prescription medications... with all their side effects.
Finding time to go in for the 25(OH)D lab test is important for a couple reasons... The first is I'm not a doctor and second, it's best to involve your PCP or neurologist, whoever knows your most recent overall medical history and prescribed medications best.
In my second career following 24 years in Naval Aviation, I worked as a technology consultant for defense clients for 14 years, living with episodic cluster headaches 6 years and then chronic cluster headaches during the last year.
I know what it's like working with cluster headaches. I worked 12 to 14 hours a day with a 2-hour round trip driving commute 6 days a week and was determined not to let my cluster headaches impact my work... I was successful until I turned chronic.
At that point I started falling asleep in the middle of team meetings with my software and electrical engineers... I would also go out to my car to suck on oxygen 2 to 3 times a day for 10 to 20 minutes at a time to abort the hits that came while working...
After a year of that, I hung up my consulting spurs and retired... My health was more important...
Take care and please keep us posted.
V/R, Batch