We've seen, many times, how differently each Sjogren's person is when it comes to symptoms and reactions to treatments. We've touched on underlying differences in body chemistry, when we talk about people with Sjogren's also having Immune deficiencies. It almost seems like there are two camps...the Sjogren's with susceptibility to everything, and the Sjogren's who never catch anything!
I'm one of the latter, and can count on one hand the number of colds I've had in the 12 years since my diagnosis, and the number is probably lower in the 30+ years of my life as an adult before diagnosis. Unfortunately, when I do catch something, it's extremely virulent and aggressive, so my "colds" look more like pneumonia with symptoms of total body failure, and one required hospitalization and O2 therapy.
What this means for me, personally, is that I'm highly susceptible to the immune strengthening properties of Vitamin C (and any other immune booster, like echinacea), and as a result, if I overindulge (and I love citrus and kiwis, so I do occasionally) I get an increase in fatigue and urticaria (my body's first indications of flare).
I conducted a little experiment, some time ago, when I was having routing blood work 4 times a year (down to twice now) wherein I documented CRP and sed rate from one blood draw, then when I was within 2 weeks of the next one, I ate one orange daily; that was the only change I made. I had the expected fatigue and itchiness, but I was actually looking for some form of documentation, which I got! My sed rate increased by 50%, and the CRP by 25%. I had had changes before, some up, some down, but the only time there was a significant change like that previously was when I started on 80 mg of Prednisone, and the drops were 30% and 15% respectively. There were no changes in IvE, so I know there was no allergic reaction involved.
I repeated the experiment a year later with very similar, if not quite as dramatic , results, but after that my blood testing was decreased and I didn't see that twice a year draws would give me the same kind of control over data, so I haven't done it since
All that to say....it's trial and error for most of us, and highly individualized.