Objectives:
Data from studies support a beneficial effect of carotenoids and vitamins on an age-related macular degeneration (AMD) risk. However, studies on the relations between blood levels of these nutrients and AMD are limited and provided conflicting results. Therefore, this review article has been conducted.

Objectives:
In postmenopausal women, vitamin D deficiency (as defined by the circulating level of 25(OH)D being below 20 ng/mL (50 nmol/L)) is a regular occurrence. The effect of vitamin D supplementation on the muscle function of postmenopausal women has been controversial. Therefore, this review article has been conducted.

Objectives:
The association between meat intake and hepatocellular carcinoma (HCC) risk is still unclear. Therefore, this review article has been conducted.

Does a higher dietary intake of meat increases the risk of hepatocellular carcinoma?

Study design:
This review article included 17 observational studies involving 2,915,680 participants, of which 4,953 cases of hepatocellular carcinoma.

Objectives:
Colorectal cancer is one of the most commonly diagnosed and deadly cancers worldwide. Epidemiological studies on the relationship between folate intake and the risk of colorectal cancer have reported inconsistent findings since folate fortification in the USA. Therefore, this review article has been conducted.

Objectives:
Dietary fats are one of the well-known stimulators of carotenoid absorption, but the effects of the quantity and the type of dietary fats on carotenoid absorption have not yet been studied systematically. Therefore, this review article has been conducted.

Do dietary fats improve the absorption of carotenoids?

Objectives:
Findings of observational studies that evaluated the association of serum vitamin D status and high blood pressure were contradictory. Therefore, this review article has been conducted.

Does a high serum vitamin D concentration reduce risk of hypertension in the adult population?

Objectives:
Vitamin D levels have been shown to be associated with diabetic retinopathy, however to date, no review has examined the relationship between vitamin D and sight threatening diabetic retinopathy (STDR) and non-sight threatening diabetic retinopathy (NSTDR). Therefore, this review article has been conducted. 

Does vitamin D deficiency (defined as 25(OH)D levels of 20 ng/mL) increase risk of diabetic retinopathy in patients with diabetes?

Objectives:
Several epidemiological studies have suggested that flavonoid intake is associated with a decreased risk of cardiometabolic disease. However, the results remained inconsistent and there is no dose-response meta-analysis for specific outcomes. Therefore, this review article has been conducted.

Is there a dose-response relationship between dietary flavonoid intake and reduced risk of cardiometabolic disease?

Objectives:
Do rheumatoid arthritis patients benefit from vitamin E supplements?

Study design:
This review article included 9 RCTs with a total of 39,845 patients.

Results and conclusions:
The investigators found that vitamin E supplements were shown to be more effective in individuals with rheumatoid arthritis for sensitive joints [MD = -1.66, 95% CI = -6.32 to -2.99, I2 = 93%, p 0.00001] and swollen joints [MD = -0.46, 95% CI = -1.98 to 1.07, I2 = 56%, p = 0.08].

Objectives:
Although recent studies comparing various dosages and intervals of vitamin D supplementation have been published, it is yet to be elucidated whether there is an appropriate dose or interval to provide benefit regarding fracture risk. Therefore, this review article has been conducted.