PhotoperiodEffect.com

7. There were at least rare cases of lupus, an autoimmune disease, diabetes, obesity, and maybe even at least one case of MS before 1800, so that doesn't fit.

As alluded to at the end of the previous reply, it's not impossible that problems did actually begin earlier, but surely far more rarely, and only amongst the very rich and very scholarly. Light, especially whitish light, is the more expensive and unusual the further you go back in history, only the Church and nobility could possibly afforded great amounts of it. Think the scholarly King Henry VIII, stereotypically fat medieval monks, and perhaps the highest Roman Aristocracy - especially if, like Caligula, they ascended to power while young. Some of the elite who could afford very expensive candles or animal oil for lamps (and possibly their servants or slaves whom they could afford to force to work long into the night) may have experienced lighting levels not all that different from moderns.

However, gas illumination quickly increased the power and sheer amount of illumination for townspeople by orders of power, and a steady logarithmic increase in our use of illumination, now compounded by video games, ubiquitous bright green fire detector LEDs, and teenagers text messaging in the middle of the night amongst many other things has continued to accelerate this trend. Every year there's more light, and more diabetes, etc, etc. Very few ancients would have been exposed to anything like so much light as the average town dweller in nineteenth century Britian or France.

We may even have one independent measure of the difference in available illumination between the 14^th century and today, and its physical effects. Collagen illnesses, which I believe the evidence now shows, are light-related, alter the shape of bones (which are made primarily of collagen) including the human skull. A recent comparison of modern and medieval skulls showed “striking” differences. To quote a BBC report: “Researchers have found that the shape of the human skull has changed significantly over the past 650 years. Modern people possess less prominent features but higher foreheads than our medieval ancestors.” [http://news.bbc.co.uk/1/hi/sci/tech/4643312.stm] The largest difference was in the “cranial vault”: moderns were fully 20% larger. Such bone overgrowth is typical of collagen disorders; better nutrition seems unlikely to alter the shape of skulls, and a few hundred years seems to quick for evolution to make such a large change. Increased illumination may seem a strange explanation of this remarkable transformation of modern skulls, but all the other explanations yet proposed are still stranger and less likely.