Depression is linked to sizeable increases in Death, Dementia, Diabetes, Heart Disease, Suicide, and Parkinson's Disease.  Research also has found that those under treatment for depression has a reduced risk of dying from heart diseasel, shrinkage of the hypothalamus area of the brain, and a somewhat lower rate of suicide.  The high rate of diabetes in the depressed certainly suggests that all depressed persons should be taking magnesium (250-500 mg/d) and vitamin D (800-1000 IU/d), since the use of these supplements have been shown to be associated with markedly reduced rates of later diabetes.

Arteriosclerosis: Depression May Cause Early Hardening of the Arteries: Depression is known to cause heart disease. In a study of 210 women, some oronary calcification was found in 49% and aorta calcification in 54%. The 53 women with a history of recurrent major depression were more than twice as likely to have any coronary calcification or calcification in the high category compared with women with a history of a single episode of depression or no depression: odds ratios (ORs) of 2.71 for high coronary calcification, and 3.39 for high aortic calcification. Coronary and aortic calcification in women with a history of major depression. Agatisa PK, et al. University of Pittsburgh. Arch Intern Med. 2005 Jun 13;165(11):1229-36. 

Death: Depression Linked to Marked Increase in Death in Elderly: In a prospective, community-based study of 5632 Italians, 65 years and older, recruited from the demographic registries, depressive symptoms using the Geriatric Depression Scale were associated with a later 66% higher incidence of fatal and nonfatal heart problems, a 149% higher cardiovascular mortality in men, and with a 102% higher total mortality in men and 43% for women at the 4-year follow-up assessment after adjusting for a vast array of potential confounding variables, including major chronic conditions. Depressive symptoms and development of coronary heart disease events: the italian longitudinal study on aging. Marzari C, Maggi S, et al. University of Padua, Italy. J Gerontol A Biol Sci Med Sci. 2005 Jan;60(1):85-92.

Dementia: Unipolar and Bipolar Depressed at Greater Risk for Dementia than Patients with Diabetes or Osteoarthritis: A Danish study of all hospitalizations in the nation followed the data for 2,007 patients hospitalized with mania, 11,700 depression, 81,380 osteoporosis, and 69,149 diabetes. Researchers calculated the risk of later hospitalization for dementia. U Copenhagen. Increased risk of developing dementia in patients with major affective disorders compared to patients with other medical illnesses. Kessing LV, Nilsson FM. J Affect Disord 2003 Feb;73(3):261-9. Ed: Depressed individuals should get treatment and should also follow the preventive strategies against Alzheimer's, which fortunately as also helpful for decreasing depression: fish oil, folic acid, B-12, vitamin D, exercise, treatment of high blood pressure, and a healthy diet of fruits, vegetables, low sodium, avoidance of mammal meats and butter, whole grains, nuts, beans, and olive or canola oil.

Dementia: Depression Somewhat Higher AD Risk: In 1,953 Alzheimer's (AD) patients and 2,093 unaffected relatives in the Research in Alzheimer's Genetic Epidemiology Study, there was an association between depression symptoms and Alzheimer's (adjusted OR, 2.13). In families where depression symptoms first occurred within 1 year before the onset of AD, the association was 357% higher (OR, 4.57), while in the families where the depression symptoms first occurred more than 1 year before the onset of AD, the association was lower: 38% (OR, 1.38). In families where depression symptoms first occurred more than 25 years before the onset of AD, there was still a modest 70% increased risk (OR, 1.7). Green RC; Cupples LA; Kurz. Arch Neurol 2003 May;60(5):753-9 

Dementia: Depression Followed by Doubled Risk of Dementia in Men: In 1,357 community-dwelling adults in the 40-year prospective Baltimore Longitudinal Study of Aging, premorbid depressive symptoms doubled the risk for dementia in men but not in women. Depressive symptoms, sex, and risk for Alzheimer's disease. Dal Forno G, Palermo MT, et al. Rome, Italy. Ann Neurol 2005;57:381-387. 

Diabetes: Depression Increases Diabetes Risk: In a 3-year follow-up study of 2,662 women, researchers found that depression was linked to higher insulin-resistance values and the onset of diabetes. This association resulted largely from abdominal obesity. Once the calculations were adjusted for "central adiposity," depression no longer predicted insulin resistance and diabetes -- except among African-American women. Diabetes was twice as high in African-American women at follow-up compared to European-American women. Susan A. Everson-Rose, Rush University Medical Center, Chicago, Diabetes Care, December 2004

Diabetes: Depression Increased Diabetes Risk 63%: In a study of 11,615 adults followed for 6 years, the quarter with the most depressed symptoms were 63% more likely to develop diabetes type 2 than the quarter with the fewest symptoms. Sherita Hill Golden, Johns Hopkins. Diabetes Care 2/2004;27:429-435. Ed: Since magnesium protects against diabetes, the magnesium supplement in my standard recommendations ( 250mg magnesium once or twice a day) would likely prevent or at least reduce this risk.

Heart Disease: Depression Risk Factor for Heart Attacks: In a 40-year follow-up of 1190 male medical students, the cumulative incidence of clinical depression was 12%. In multivariate analysis, the men who reported clinical depression were at significantly greater risk for subsequent coronary heart disease (RR, 2.12) and myocardial infarction (RR, 2.12). The increased risk associated with clinical depression was present even for myocardial infarctions occurring 10 years after the onset of the first depressive episode (RR, 2.1). Depression is a risk factor for coronary artery disease in men: the precursors study. Ford DE, Mead LA, Chang PP, Cooper-Patrick L, Wang NY, Klag MJ. Johns Hopkins. Arch Intern Med. 1998 Jul 13;158(13):1422-6.

Heart Disease: Increased Risk of Death after Coronary Artery Bypass if Depressed: In 817 patients there were 122 deaths (15%) in a mean follow-up of 5.2 years. 310 patients (38%) met the criterion for depression: 213 (26%) for mild depression and 97 (12%) for moderate to severe depression. Survival analyses, controlling for age, sex, number of grafts, diabetes, smoking, left ventricular ejection fraction, and previous myocardial infarction, showed that patients with moderate to severe depression at baseline [HR] 2.4; p=0.001) and mild or moderate to severe depression that persisted from baseline to 6 months (adjusted HR 2.2; p=0.015) had higher rates of death. Duke Univ. Depression as a risk factor for mortality after coronary artery bypass surgery. Blumenthal JA, Lett HS, Babyak MA, White W, Smith PK, Mark DB, Jones R, Mathew JP, Newman MF; NORG Investigators. Lancet. 2003 Aug 23;362(9384):604-9.

Heart Disease: Serotonin-Mediated Platelet Activation in Depressed Increases Heart Death: Antidepressant counter the higher level of serotonin-activated platelet activation found in heart disease patients with depression and lower the otherwise higher death rate in these patients. Depression is an independent risk factor for heart disease. Increased coronary events in depressed cardiovascular patients: 5-HT2A receptor as missing link? Schins A, Honig A, Crijns H, Baur L, Hamulyak K. Psychosom Med 2003 Sep-Oct;65(5):729-37

Hippocampus Smaller in Depression: In a study of 31 adults with recurrent MDD in full remission, and 57 healthy controls, eight patients were medication-naive, and twenty-three MDD patients were off antidepressant medications for a mean of 30 months at the time of the MRI study. Patients showed smaller total and posterior hippocampal volume relative to controls. Reduced hippocampal volume in unmedicated, remitted patients with major depression versus control subjects. Neumeister A, Wood S, et al. Yale University. Biol Psychiatry. 2005 Apr 15;57(8):935-7.

Menopause Earlier in Smokers and Depressed for Different Reasons: Women with depression have earlier menopause on average. In a study of women with major depression, serum FSH levels were higher in women with a history of depression, while inhibin B levels did not differ between groups. Body mass index and age were significantly and inversely related to serum inhibin B levels. Smoking history had a significant negative association with inhibin B levels. Thus, smoking has a direct negative effect on ovarian reserve, as suggested by decreased serum inhibin B levels. In contrast, effects of depression on the reproductive axis may occur at the level of the pituitary and/or hypothalamus rather than at the gonadal level, as suggested by increased serum FSH levels. The influence of depression, body mass index and smoking on serum inhibin B levels in late reproductive aged women. Lambert-Messerlian GM, et al. Brown Medical School, Providence, RI. J Clin endocrin Metab 2006 Jan 31.

Parkinson's: Depressed Three Times More Parkinson’s: Parkinson’s patients’ brains have a lowered level of the neurotransmitter serotonin. Low levels of serotonin play a key role in depression. Serotonin also acts to modulate the release of the neurotransmitter dopamine in the brain. Because the level of dopamine activity is decreased in Parkinson’s, researchers believe the amount of serotonin activity is also decreased in compensation. That reduction increases the risk of depression. Because the reduced serotonin activity already exists before any motor symptoms begin, the risk of depression is also increased long before any Parkinson’s symptoms become apparent. Schuurman, Maasstricht, Netherlands, Neurol 5/28/02.