The first issue that we must address is that Europeans in the 17th, 18th, and even 19th centuries did not see health and medicine as we do today. Accordingly, a large emphasis was placed on weather, temperature, and other aspects that we wouldn't place too much of an emphasis upon today. Unfortunately, while I have neither the data nor the scientific knowledge to tell you whether Europeans really did suffer poor health in India, I can tell you definitively that these people personally believed the tropical climate was detrimental to their well being. Interestingly, in the case of India, such beliefs weren't limited to Europeans, but were voiced occasionally by travelers and foreigners from all sorts of places.

An excellent early example of non-Europeans struggling to adapt to the Indian climate comes from the earliest members of the Mughal dynasty. When Babur (a central Asian ruler and founder of the dynasty that would rule India for the next two centuries) first arrived in the Indo-Gangetic Plain, his Afghan commanders complained bitterly of the Indian heat, and many begged to return to Afghanistan with their booty (ultimately, many did give up the Indian heat and return to Afghanistan, despite Babur's wishes to the contrary). Abd al-Qadir Badaruni, a later court historian who wrote Babur's histories complained that the heat caused the "brain to boil in the cranium." Ultimately, the Mughals did adapt somewhat to the North Indian heat, but the emperors continued to travel only in shaded palanquins and had constant supplies of water available for long journeys. Indeed, none of the Mughal Emperors, even those born in India, made it a habit to lounge under the hot Indian sun.

So, we have established that non-European visitors also suffered in the Indian climate, but what did actual Europeans think of the weather? Francois Bernier, a French physician who served the Mughal prince Dara Shikoh, wrote that the heat left him "parched and withered," "covered entirely with small red blisters," and sweating "like a sieve," unable to replenish himself. Similarly, the Dutch merchant Francisco Pelsaert noted that "men could scarcely breath" under the hot Indian sun. Benier and Palsaert's experiences were about average for European travelers in India, however, they did not limit their observations to themselves. To the contrary, European travelers were as quick to note the inability of native Indians to tolerate the weather as they were to note their own discomforts. Bernier (incorrectly) praised the hot Indian climate for turning people away from alcohol and rendering veneral diseases less serious, but he also noted that the people of India, unlike those of colder climates, were weak and feeble, an "unremitting malady" brought on by the harsh weather. Indeed, while travelers like Bernier were outspoken in their inability to tolerate the Indian Heat, they absolutely believed that the heat was as damaging to the natives as it was to themselves. This was ultimately an observation rooted in both scientific misunderstanding (most Indians were poor and unable to acquire the food required to maintain a healthy physique), as well as racist sentiment. Men like Bernier and Palsaert complained that Indians were weak and lazy, and performed little work unless compelled to by the whip; the Italian explorer Giovanni Careri complained that Indians were used to wasting their meager wages, "living idly" as long as they lasted.

Such sentiments lasted well into the 18th and 19th centuries, with white officials in the East India company actively avoiding hard labor, and conducting their day to day activities specifically in order to avoid the hot sun. Even EIC military officers got most of their work done early in the morning, spending most of the day indoors, fanned by Indian servants. White travelers and officials really did, by their own admission, suffer quite a bit in the Indian climate, and genuinely felt that such heat was bad for one's health. Even if this suffering was indeed legitimate, it did not prevent Europeans from using arguments rooted in the Indian climate and its effects upon the body in order to exploit native labor.