Table 5.
Protective effects of carotenoids against diabetic complications—clinical evidence.
| Carotenoid name | Administration | Experimental design | Treatment | Duration | Results | References | |
|---|---|---|---|---|---|---|---|
| Upregulation | Downregulation | ||||||
| Lutein and zeaxanthin | Oral, dietary supplement | Case control in 30 patients with NDR | 6 mg lutein / day 0.5 mg zeaxanthin/day | 3 months | 1. Increased serum levels of lutein and zeaxanthin 2. Increased visual acuity 3. Improved CS | Decreased foveal thickness | (97) |
| Lutein and zeaxanthin | Oral, dietary supplement | Dietary intervention in 60 patients with T2DM | lutein (10 mg), zeaxanthin (2 mg) and meso-zeaxanthin (10 mg) once a day | 2 years | 1. Increased central foveal thickness 2. Improved macular function assessed by mfERG | (98) | |
| Lutein and zeaxanthin | Oral, dietary supplement | Double-blind RCT in patients with T1/2 DM with no retinopathy or mild to moderate non-proliferative retinopathy | A multi-component capsule containing lutein and zeaxanthin, antioxidants and selected botanical extracts; twice daily | 6 months | Improved visual function and MPOD | 1. Reduction in the serum levels of HDL-C, LDL-C and triglycerides 2. Decreased hsCRP levels 3. Reduction in DPNSSs | (99) |
| Lutein | Oral, dietary supplement | Double-blind RCT in 15 patients with NDR | 1 capsule daily containing 10 mg of lutein | 36 weeks | Increased CS at four spatial frequencies and improved CS at 3 cycles/degree | (100) | |
| Lycopene | Oral, dietary supplement | Double blind RCT in 16 patients with T2DM | 10 mg/day | 2 months | 1. Increased serum lycopene levels 2. Increased ratio of TAC to MDA | 1. Level of serum IgG reduced when serum concentration of lycopene increased 2. Insignificant decrement in serum ox-LDL and IgG levels | (101) |
| Lycopene | Oral, dietary supplement | Parallel RCT in 15 patients with T2DM | 250 ml tomato juice twice daily | 4 weeks | 1. Almost 3-fold increase in plasma lycopene levels 2. A 42% increment in the lag time in the isolated LDL oxidation by copper ions | Decreased plasma CRP levels | (102) |
| β-Carotene | Oral, food | Double blind, crossover RCT in 51 patients with T2DM | Fortified synbiotic food containing 0.05 g β-carotene | 6 weeks | Elevated plasma nitric oxide and GSH levels | Decreased levels of insulin, HOMA-IR, HOMA-B, triglycerides and VLDL-C and TC/HDL-C ratio | (103) |
| β-Carotene, α-tocopherol | Oral, dietary supplement | Double-blind 2×2 factorial design RCT in 29,133 male-smokers (1,700 with T2DM—662 diagnosed with first-ever macrovascular complication) | 1 capsule daily, either containing α-tocopherol (50 mg/d), β-carotene (20 mg/d), or both | 3 years | No effect | No effect | (104) |
| Carotenoids | Oral, dietary supplement | Parallel RCT in 21 patients with T2DM | 40 g green banana biomass added to habitual diet daily | 6 months | Increased carotenoid content in the LDL-C particles, i.e., enhanced prevention of LDL-C oxidation | Reduced levels of TC, non-HDL-C, glucose and HbA1c | (38) |
NDR, nonproliferative diabetic retinopathy; CS, contrast sensitivity; T2DM, type-2 diabetes mellitus; mfERG, multifocal electroretinography; RCT, randomized controlled trial; MPOD, macular pigment optical density; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; hsCRP, high-sensitivity C-reactive protein; DPNSSs, diabetic peripheral neuropathy symptom scores; TAC, total antioxidant capacity; MDA, malondialdehyde; IgG, immunoglobulin G; ox-LDL, oxidized-LDL; GSH, glutathione; HOMA-IR, homeostatic model assessment of insulin resistance; HOMA-B, homeostatic model assessment of β-cell function; VDL-C, very-low-density-lipoprotein-cholesterol; TC, total cholesterol; HDL-C, high-density lipoprotein cholesterol; HbA1C, glycosylated hemoglobin.