Modern definitions of diseases often are incompatible with ancient Indian definitions. Diabetes is not a disease, but a group of diseases broadly divided into three classes, and associated with or leading to a lot of other diseases such as blindness, heart disease, urinary problems, etc etc. It is not possible to associate astrological factors with all modern medical concepts.
There are cases in which Saturn and even Mars are connected with Diabetes. Shambhu Hora Prakash (chapter 14) associates uninary problems sometimes related to diabetes with 5H associated with Sun-Venus-Saturn, or 10H associated with Mars-Saturn. Diabetes related to eyes, heart, etc will have association with other houses and planets. It is better to deal with diabetes patients on the basis of individual charts and current dashaas in those charts, and D-30 should also be used together with D-1.
But an overwhelming majority of diabetes cases (over 80%) are related to affliction of Jupiter, Venus and Libra. However, in actual case studies this generalisation is of not always helpful because of exceptions and because lots of complications arising out of Diabetes may not be related to Jupiter, Venus or Libra.
Astrodatabank contains some charts with Jupiter in own sign and with rajayoga (1L + 4L), but conjoined with debilitated planet. Debilitated planet destroys the effects of exaltation or own sign, but makes that exalted or svagrihi planet equivalent to neutral planet, yet we find Diabetes when raja yoga giver svagrihi Jupiter sits with a debilitated planet. But without D-30, we cannot deduce definite results on the basis of D-1 alone.
Glucose (not diabetes, but normal sugar) is related to Jupiter because it is sweet and is the essential component of sweet. Venus is related to acid (BPHS) and therefore Venus regulates the acid balance of body. Abnormal acidity is caused by Venus, often leading to insulin imbalance and diabetes (cf. http://www.budwigcenter.com/acid-ph-dangers.php). Many other complications related to diabetes are also due to abnormal acidity (wrong pH). But abnormal acidity due to afflicted Venus results in Diabetes only when Jupiter is also afflicted resulting in sugar imbalance. Although Vrish is also lorded by Venus, basic own sign of Venus is actually Libra according to BPHS. If Venus or Jupiter is much more afflicted, then other complications may also arise. Hence, generalisations should not be relied on blindly, and actual chart reading of D1 and D30 is the only sure shot to ascertain the actual affliction of the native.
Diabetes is called Madhumeha in classics of Jyotisha, and therefore is linked to excess sugar (Madhu) in urine (meha) which is due to excess sugar in blood. 2H or 7H does or any house not necessarily cause Diabetes, they are related to all sorts of diseases and other things. In 80% cases, Diabetes is a special case produced by combination of afflictions of Venus (abnormal acidity affecting insulin), Jupiter (affecting blood sugar level) and Libra which is natural own sign of Venus. Variations in degree of afflictions of these elements give rise to variations in the diseases and extra complications which overwhelm the basic causes related to Venus and Jupiter. These findings are not deduced from medical reports but from astrological case studies of large number of horoscopes. Venus affects Amla (acidity) according to BPHS, and the latter affects insulin level. It is only the reference to insulin which is from medical terminology, but there is no other way in which astrological property of Venus (ie, acidity) can be connected to Diabetes caused by Venus as manifest in large number of horoscopes. Phaladeepika summarises effects of different planets on diseases, and puts Diabetes under Venus, which is found to be true in majority of diabetes cases because Venus regulates acid level and therefore insulin level.
10% of Diabetes cases are due to Type-1 (malfunction in insulin pruduction in pancreas) plus Type-3 of Diabetes, while 90% cases of Diabetes are due to inability of cells to respond to insulin, and in these cases insulin production and distribution is normal but the patient suffers from Diabetes. Use any search engine to get technical information. This Wikipedia article mentions this fact :-
http://en.wikipedia.org/wiki/Diabetes_mellitus states : "Globally, as of 2013, an estimated 382 million people have diabetes worldwide, with type 2 diabetes making up about 90% of the cases."
and gives two links to authoritative sources for this data. The same article also mentions :-
"Type 2 DM begins with insulin resistance, a condition in which cells fail to respond to insulin properly."
Kshaara as "Alkali" is modern Sarkaari term, not related to its ancient meaning. Kshaara is derived from Kshar, which means perishable, dissolving material, ie salt and not alkali. The taste of alkali is BITTER (Tikta) and not saline, and the taste of acid is SOUR (Amlaka). Tikta is the taste of Mars. Bile from liver is alkaline, hence it should be related to Mars. BPHS has no connection with chemistry or physics or biology. Vedic Jyotisha does not deal with molecular structure or chemical composition, it deals with supernatural effects of planets on living creatures, and on phenomena like weather etc which affect living creatures. Without forgetting modern science, it will be impossible to get the mindset required to understand ancient texts.
But in 20% cases, Jupiter and Venus are not the main factors, and other planets take precedence, because Diabetes is associated with many other diseases which are TRIGGERED by Diabetes. But these cases are in minority, which proves that other planets trigger the side effects of Diabetes while Venus and Jupiter are chief factors of Diabetes itself.