Our data suggest that (1) the majority of elderly type 2 diabetes patients may have low magnesium intake; (2) about one-third of elderly diabetes patients had hypomagnesaemia; (3) low magnesium intake was associated with metabolic abnormalities and depression; (4) magnesium intake was related to high physical activity level and demonstrated lower serum magnesium levels. However, serum magnesium was not significantly associated with metabolic parameters.
In general, dietary magnesium does not meet the DRI for elderly subjects and may be prone to chronic latent magnesium deficiency [41
]. Daily magnesium intake for males and females above 50
years of age was 326
mg and 255
mg, respectively, in the United States. Furthermore, 60-62% of middle-aged to elderly people do not meet the DRI for magnesium [42
]. The average magnesium intake for male and female elders was 279
mg and 227
mg, respectively, according to data from the Nutrition and Health Surveys in Taiwan [41
]. These data indicated that they are at least 87% of the population in Taiwan do not meet the DRI for magnesium. In our data, daily consumption of magnesium in male and female elderly type 2 DM patients was only 253
mg and 189
mg magnesium, respectively. This indicates that 89% of our patients do not meet the DRI for magnesium.
It is generally accepted that magnesium deficiency is closely related to metabolic syndromes. Increased dietary magnesium intake and/or magnesium supplementation may improve metabolic syndromes and type 2 DM [14
]. Our data also revealed that lower magnesium intake was correlated with metabolic syndromes. It affects HDL, triglyceride, WC, BMI, and body fat percentage. In addition, systolic and diastolic blood pressure showed marginal inverse relationships with magnesium intake. The overall prevalence of metabolic syndromes in these rural-dwelling elderly type 2 DM patients was 74% which was much higher than rates reported in two previous studies on healthy older adults (40%) [14
]. However, the relationships of magnesium intake with blood glucose and lipids were inconsistent. Thus, increased magnesium intake may improve metabolic control in patients with metabolic syndromes.
Depression is the fourth-leading cause of disability worldwide according to the World Health Organization [44
]. Prevalence rates of depression are between 5% and 10% [45
], whereas it is estimated to be about 12% to 18% in patients with diabetes [46
]. Moreover, 31% of elderly diabetes was found to have severe depressive symptoms [47
]. This finding was confirmed and 30% of elderly diabetes patients had depression, particularly in those with low magnesium intake. Indeed, magnesium deficiency has been independently associated with depressive symptoms [13
]. A recent randomized, equivalent trial suggests that oral magnesium supplementation is as effective as imipramine in the treatment of depressed elderly diabetes with hypomagnesemia [20
]. Thus, increasing dietary magnesium intake or magnesium supplementation for elderly patients with diabetes may benefit the treatment of depression.
A review study indicated that 14-48% of diabetes suffered from hypomagnesaemia [48
]. In the present study, the prevalence of hypomagnesaemia was about 37%. In addition, we found that magnesium intake had a significant positive relationship with energy intake and protein intake. Moreover, lower intake of energy and magnesium was correlated with a higher prevalence of hypomagnesemia. In the present study, prevalence of hypomagnesemia for the energy intake
kcal/kg groups were 40%, 36%, and 32%, respectively. Likewise, lower intake of protein and magnesium was associated with a higher prevalence of hypomagnesemia. Prevalence of hypomagnesemia for the protein intake
g/kg groups were 43%, 27%, and 34%, respectively. However, 89% of the elderly diabetes patients had a magnesium intake which was less than the DRI, however, the prevalence of hypomagnesaemia was only 37%. Therefore, more than 50% of our patients with a magnesium intake less than the Taiwan DRI could not be identified as hypomagnesemia (low serum magnesium <0.75
mmol/L). Therefore, our results revealed that serum magnesium was not correlated well with metabolic parameters and depression as shown in a previous study [49
]. Many studies showed that low magnesium intake is associated with certain degrees of diabetes risk, metabolic control and cardiovascular diseases. Serum magnesium may not be a good marker and may be inaccurate to correlates with magnesium status. However, hypomagnesemia could indicate a higher possibility of critical situations associated to diabetes, metabolic syndromes or cardiovascular diseases. Future clinical trials need to reveal relationships of serum magnesium, intracellular magnesium levels with various diseases.
The relationship between magnesium status and physical activity has received much attention in the past decade [11
]. Our data clearly indicated that the low physical activity group had lower magnesium intake. Magnesium intake was about the same in the high and moderate physical activity groups. However, the high physical activity group had a significantly lower serum magnesium levels. In our data, prevalence of hypomagnesemia in the low, moderate and high physical activity groups were 27%, 31% and 49% respectively. Obviously, the high physical activity groups also had a significantly higher prevalence of hypomagnesemia when compared with that in other two physical activity groups. Thus, high intensity physical activity with inadequate magnesium intake seems to increase the risk of hypomagnesemia. This may be partly due to increased magnesium loss in perspiration (especially when working or exercising in hot environments) and in urine [50
]. This could result in increased magnesium excretion and might increase the need for higher magnesium intake. When magnesium intake is insufficient, physical activity will exacerbate the magnesium deficiency [51
]. Increased dietary magnesium intake or magnesium supplementation has beneficial effects on physical performance in magnesium-deficient individuals [52
]. Hence, for elderly diabetes patients with high physical activity and low serum magnesium, it is necessary to increase dietary magnesium intake or magnesium supplementation.
There were several limitations of this study. First, the analyses were highly dependent on self-reported dietary intake and lifestyle data. Overestimation, underestimation, and poor recall might therefore have confounded the results. Fortunately, these elderly DM patients lived in rural areas and mostly of them had a simple lifestyle and eating patterns. The use of traditional quantitative tools, food models, food pictures and photos helped these elderly patients to recall the amount of consumed food and may also increase the effectiveness of the 24-hour recall. Moreover, questionnaires were also used to valid dietary patterns during the previous week. Second, serum magnesium may not be sufficient for indicating magnesium deficiency [21
]. Therefore, the majority of patients (>89%) with less than the DRI magnesium intake were not identified as magnesium deficiency from their serum magnesium levels. Further investigation will be warranted.